Is it regarded as immoral to marry a young girl in Islam given that prophet Muhammad married Aisha when she was 6-7 and had her consummated when she was around 10? Generally, is everything Muhammad did considered as desirable, expected and/or good behavior for Muslims nowadays?
It is permissible to marry a young girl. However, there are two views on whether intercourse is permissiable. One view says they can have intercourse if she reaches the age of 9, while another view says intercourse should not happen before she is ready for it, and this seems to be the majority view of Hanafi, Maliki, and Shafi'i schools of though.
The fact that it is permissible to marry a young girl does not mean that it is permissible to have intercourse with her; rather that should not be done until she is able for it. For that reason the Prophet (peace and blessings of Allaah be upon him) delayed the consummation of his marriage to ‘Aa’ishah. Al-Nawawi said: With regard to the wedding-party of a young married girl at the time of consummating the marriage, if the husband and the guardian of the girl agree upon something that will not cause harm to the young girl, then that may be done. If they disagree, then Ahmad and Abu ‘Ubayd say that once a girl reaches the age of nine then the marriage may be consummated even without her consent, but that does not apply in the case of who is younger. Maalik, al-Shaafa’i and Abu Haneefah said: the marriage may be consummated when the girl is able for intercourse, which varies from one girl to another, so no age limit can be set. This is the correct view. There is nothing in the hadeeth of ‘Aa’ishah to set an age limit, or to forbid that in the case of a girl who is able for it before the age of nine, or to allow it in the case of a girl who is not able for it and has reached the age of nine. Al-Dawoodi said: ‘Aa’ishah (may Allaah be pleased with her) was reached physical maturity (at the time when her marriage was consummated).
It should be noted that al-Shaafa’i and his companions said: It is preferable for fathers and grandfathers not to marry off a virgin until she reaches the age of puberty and they ask her permission, lest she end up in a marriage that she dislikes. What they said does not go against the hadeeth of ‘Aa’ishah, because what they meant is that they should not marry her off before she reaches puberty if there is no obvious interest to be served that they fear will be missed out on if they delay it, as in the hadeeth of ‘Aa’ishah. In that case it is preferable to go ahead with the marriage because the father is enjoined to take care of his child’s interests and not to let a good opportunity slip away.
The version of the story mentioned in this question is actually very debatable. A lot of scholars believe that Lady Aisha was much older than that; more like 18 or 19 years of age.
Anyway, I think this subject needs more research. And to answer your question; I personally believe that marrying underage girls is something that is HIGHLY immoral.
قال ابن شبرمة : لا يجوز إنكاح الأب ابنته الصغيرة إلا حتى تبلغ وتأذن ، ورأى أمر عائشة رضي الله عنها خصوصاً للنبي صلى الله عليه وسلم " .
Ibn Shubrumah said: It is not permissible for the father to marry off his young daughter except when she reaches puberty and gives permission.” And he was of the view that the matter of A’ishah(radi Allahu anha) was exclusively for the Prophet(sallallahu alayhi wa sallam).(source of Arabic text: saaid.net)
وذكر عن ابن شبرمة رحمه الله أنه قال : لا يجوز أن يزوج الصغيرة التي لم تبلغ أبداً ؛ لأننا إن قلنا بشرط الرضا فرضاها غير معتبر ، ولا نقول بالإجبار في البالغة فهذه من باب أولى
And it was narrated that Ibn Shubrumah(may Allah have mercy on him) said: “It is not permissible for the young girl to be married off, because if we say that consent is a principle of its validity, then her consent is not counted, and we do not say she should be forced into a marriage when she has reached puberty, so it applies all the more here.”(source of Arabic text: saaid.net)
Some scholars disagree and say that it is permissible.
As for which view is right, I’m not a scholar, but Ibn Hazm has said:
“..taqlid is haram, and it is not permissible for anyone to follow the words of someone without proof.
The proof of that is: Allah ta’ala’s saying: “Follow, [O mankind], what has been revealed to you from your Lord and do not follow other than Him any allies. Little do you remember.”(Qur’an 7:3) and His(ta’ala) saying: “And when it is said to them, "Follow what Allah has revealed," they say, "Rather, we will follow that which we found our fathers doing.””(Qur’an 2:170), and Allah ta’ala said, praising a people who did not do taqlid: “So give good tidings to My servants who listen to speech and follow the best of it. Those are the ones Allah has guided, and those are people of understanding.”(From Qur’an 39:17-18)…”(source: the book Nabdhah Kafiyah by Ibn Hazm)
Disclaimer: As with all my answers, I am not giving a fatwa. I share what I know of Islamic scripture, historical events and opinions of scholars, and translations of them, and sometimes my opinion, and they may or may not be the correct answer to the question, and I may or may not have interpreted them correctly as being relevant. Scriptural texts posted in English are a translation from the original Arabic and may not be completely accurate or encompass the full meaning of the original.