As one who is in pursuit of the truth regarding Islam’s laws and the viewpoints of the late leader of the Islamic Revolution, Imam Khomeini, it is of dire importance that you rely only on authentic sources and official websites for information and answers.
As the final and complete divine religion, Islam addresses all of man’s needs, sexual ones being one of them, and for the fulfillment of this need, has prescribed marriage with the opposite gender only, and under certain conditions.
Also, Islam considers preparing the grounds for the marriage of individuals, especially youth who need assistance and aid in this regard, everyone’s responsibility and a religious duty upon their parents and grandparents, yielding great rewards from Allah (swt) for those who do help out. At the same time though, Islam doesn’t permit all marriages unconditionally; it only validates marriages that meet certain conditions and criteria, namely: Islam has forbidden any form of sexual pleasure with non-humans (animals) and has specified punishments for those who may do so. These statements have been clearly made by Imam Khomeini and other jurisprudents, leaving no room for any doubt.
Another point that must be made is that in Islam, there is no age limit for marriage and it has left this matter to the two sides of the marriage (in the case of them being religiously of age/pubescent/baligh) or to their supervisors (in the case of them not having reached the required age). Thus, the marriage of minors has to be with the permission of their supervisors, who presumably will only allow it if it is to their benefit or at least not to their harm. Also, in order to prevent others from sexually taking advantage of children, it has legislated conditions that if aren't met, lead to the punishment of the individual.
It is very important to know that the maraje’ and jurisprudents of Islam bear the great responsibility of deriving Islamic law from its sources. Of course, do note that in Islamic fiqh, all subjects have primary and original and main rulings if you may, and also, can have secondary ones. That which books of Islamic law or risalahs are responsible for mentioning, are the primary ones, the permissibility of marrying a girl child being one of those main and primary ones. At the same time, this issue has a secondary ruling that comes into play whenever it applies, and that is if sexual pleasure hurts or bothers her physically or mentally, Islam will no longer see it permissible, even though it would have been okay under normal circumstances. This is something all Islamic scholars agree on.
Some of the things attributed in your question to Islam and the great faqih and scholar of our time, Imam Khomeini, are totally false! It is expected that one who is truly after the truth to refer to the authentic sources and official websites for the right facts on Islamic law and the late leader of the Islamic revolution, Imam Khomeini. At the same time, some of the things you quoted are true and need some clarification in order to illuminate the truth of the matter.
Islam is the final and complete divine religion to man. One of the features of this religion is that it addresses all of man’s needs and has guidelines for a prosperous life in all aspects. One of these undeniable and inevitable needs is lust, which if not identified, taken care of and dealt with properly, will entail many individual and social problems and complications. These problems can be seen throughout history, in those societies that were unfamiliar with the teachings of the prophets who would resort to the wrong solutions for satisfying this need, such as marriage with their maharem (mothers, sisters, etc.), sodomy, bestiality, masturbation, etc. In satisfying this very important need, Islam has prescribed marriage with the opposite gender, with certain conditions being met. Islam looks at marriage as something good and praiseworthy that one needs in order to preserve his/her religion. The reason being that through getting married and answering his sexual needs through this means, a youth who has reached the age in which he has full sexual effervescence prevents moral corruption and distraction, bringing peace of mind and paving the way for his/her spiritual and intellectual development.
The importance of marriage in Islam is to the extent that providing those who need it, especially youth in full sexual effervescence, with the necessities for doing so and aiding them and setting the stage for their marriage has been made everyone’s responsibility, and the religious duty of their parents and grandparents.
Therefore, if there are hadith that say it is better for girls to get married and be in their husbands’ home before their first menstrual period (puberty), or that the father who sends his daughter to her husband’s home before she experiences menstruation has salvation, they are for the encouragement of early marriage and to signify the important role it plays in moral corruption prevention. It is on this basis that Islam urges marriage as soon as possible and assures us not to worry much about financial problems and poverty.
Although in Islam’s eyes, the one way to satisfy sexual needs is through marriage, at the same time it has set certain conditions and hasn’t permitted marriage unconditionally. Some of these conditions are:
1- Islam forbids any sexual acts with animals and has specified punishments for those who do so. Imam Khomeini and other jurisprudents say in this regard: “Anyone who commits intercourse with an animal first receives the ta’zir punishment (around 25 lashes). If he repeats it, he is to be executed after the fourth time. Also, the animal intercourse has been performed with must be slaughtered (if it is of the animals whose meat is halal to eat) and its meat cannot be eaten [by anyone], and the person committing the sin has to compensate for the lost animal and pay back its owner. This is another form of punishing that person, in addition to other bodily punishments, he has to suffer a financial penalty as well. Considering all of the above, it becomes clear that it is nothing more than a false accusation to say that Islam allows bestiality; something that any person with the least knowledge on Islam affirms.
2- Islam sets no age limit for marriage and has left it to those getting married (if they have come of age/are balegh) or their supervisors (if they are minors religiously). What you have said about “young boys or girls in full sexual effervescence are kept from getting married before they reach the legal age of majority” is very strange to us, especially since you haven't cited any sources for your claim. This is while all Islamic sects, Shia and Sunni, see the marriage of minors as permissible, of course with the permission of their supervisors (father or paternal grandfather in the case of there not being a father). It goes without saying that just because the marriage of or with minors is permissible, it doesn’t mean that all sexual acts can be practiced with them; some acts depend on the wife having reached a certain age, preventing any potential physical or mental harm. In the case of the man not observing these conditions and harming the girl through intercourse when he isn't allowed to, in addition to the girl becoming permanently unlawful to him, there will be heavy financial penalties awaiting him that Islamic jurisprudents have mentioned in their risalahs or books on Islamic law.
It should also be noted that just because marriage with a minor is permissible, it doesn’t mean that it is something that Islam encourages or has obliged; all it means is that if for whatever reason one does get married to a minor, he hasn’t committed a haram act. What needs to be done is of him to meet the criteria and conditions Islam has specified to prevent all harms and potential problems.
It is also noteworthy that:
First of all, this ruling (marriage with a child) must be always be considered with the authority Islam has granted the child’s caring supervisor. They are fully aware that they should allow such a thing to happen only and only if it is somehow to the benefit of the child.
Secondly, Islamic jurisprudents cannot issue fatwas from themselves, they are obliged to issue fatwas derived from the Quran and tradition using authentic principles and standards for their inferences, even if such a fatwa is to the distaste of others or might not be well received and acted upon by them.
The laws listed in fiqhi books are to teach us what the rulings of things that take place for us are and the ruling being discussed in this article is about the permissibility of such marriages per se. At the same time though and despite its initial permissibility, there are hadith that emphasize it is better not to get married to those who haven't reached puberty yet, let alone those who are in there first years and may even be nursing.
Therefore, people haven't been encouraged to do so, and if such marriages do ever take place, they are exceptional cases meant for specific purposes. It can be said there aren't any instances of this marriage today and would seldom take place in the past and if they did, there were other good intentions behind them, such as a baby who had lost all her family in an incident and someone else would marry it to take care of and supervise it.
Third of all, as high ranking Islamic experts, jurisprudents and maraje’ bear the heavy responsibility of deriving Islamic law from its authentic sources. What should be kept in mind is that according to Islamic fiqh, all subjects can have two series of rulings; primary and main ones, and secondary ones. What is listed in risalahs is the primary ruling of issues, in our case, the initial permissibility of marriage with a child. Nevertheless, this issue has a secondary ruling as well, that comes into play whenever it applies, and that is that whenever sexual pleasure leads to physical and/or mental harm to the minor, its permissibility is revoked; this is something all scholars agree on.
You had also quoted some things from “The Little Green Book” which we haven't heard of and don’t know of and ask you to only refer to substantial and reliable books when learning of the sayings of great ulema.
For further information on Islam’s viewpoint regarding marrying nursing children, see Question 7554 (website:7619) Marrying a nursing girl.
 Majlisi, Muhammad Taqi, Biharul-Anwar, vol. 100, pp. 214-219: [الأمالی للشیخ الطوسی] بِإِسْنَادٍ الْمُجَاشِعِیِّ عَنِ الصَّادِقِ ع عَنْ آبَائِهِ ع قَالَ قَالَ رَسُولُ اللَّهِ ص مَنْ تَزَوَّجَ فَقَدْ أَحْرَزَ نِصْفَ دِینِهِ فَلْیَتَّقِ اللَّهَ فِی النِّصْفِ الْبَاقِی
 Al-Kafi, vol. 5, pg. 336: بَابُ مَا یُسْتَحَبُّ مِنْ تَزْوِیجِ النِّسَاءِ عِنْدَ بُلُوغِهِنَّ وَ تَحْصِینِهِنَّ بِالْأَزْوَاجِ ،حدیث 1- مُحَمَّدُ بْنُ یَحْیَى عَنْ أَحْمَدَ بْنِ مُحَمَّدِ بْنِ عِیسَى عَنْ بَعْضِ أَصْحَابِهِ عَنْ أَبِی عَبْدِ اللَّهِ ع قَالَ مِنْ سَعَادَةِ الْمَرْءِ أَنْ لَا تَطْمَثَ ابْنَتُهُ فِی بَیْتِه
 Nur:32 وَ أَنْکِحُوا الْأَیامى مِنْکُمْ وَ الصَّالِحینَ مِنْ عِبادِکُمْ وَ إِمائِکُمْ إِنْ یَکُونُوا فُقَراءَ یُغْنِهِمُ اللَّهُ مِنْ فَضْلِهِ وَ اللَّهُ واسِعٌ
 Tahrirul-Wasilah, vol. 2, pg. 496, chapter: Intercourse with animals and corpses, issues 1 and 3; Fazel Lankarani, Mohammad, Tafdilul-Shariah, chapter: Al-hudud, pg. 716.
 Al-Kafi, vol. 5, pg. 398 عَنْ أَبِی عَبْدِ اللَّهِ أَوْ أَبِی الْحَسَنِ ع قَالَ قِیلَ لَهُ إِنَّا نُزَوِّجُ صِبْیَانَنَا وَ هُمْ صِغَارٌ قَالَ فَقَالَ إِذَا زُوِّجُوا وَ هُمْ صِغَارٌ لَمْ یَکَادُوا یَتَأَلَّفُوا
 Adopted from Question 7554 (website: 7619) Marriage with a nursing girl.