Age of Marriage Under Hindu Law
due to the situation in kashmir, many hindus harbor ill will towards muslims. as a consequence, some of them attack prophet muhammad (peace be upon him) by accusing him of being a pedophile. yet, a quick look at the hindu religious texts is enough to refute them. in the hindu religious scripture known as the manu-smriti, we read:
gautama (18-21).— a girl should be given in marriage before puberty.
vashistha (17.70).— out of fear of the appearance of the menses, let the father marry his daughter while she still runs about naked. for if she stays in the home after the age of puberty, sin falls on the father.
bodhayana (4.1.11).— let him give his daughter, while she still goes about naked, to a man who has not broken the vow of chastity and who possesses good qualities, or even to one destitute of good qualities ; let him not keep the maiden in his house after she has reached the age of puberty.
(manu ix, 88; http://www.payer.de/dharmashastra/dharmash083.htm)
in an article entitled “child marriage in nepal”, we read:
in the ancient hindu scriptures of 400 to 100 bc, there are strict moral laws that enjoin the father to marry off his daughter at a very young age. these religious texts indicate that the best age for a girl to get married is between is 8 and 10.
it has been also mentioned that a girl should not wait for marriage more than three years after attaining puberty, and if she is not given by then in marriage by her father, the texts even instruct her to get married on her own. such religious texts (the bishnu sutra and gautam sutra) direct the father to marry his daughter within three weeks of attaining puberty, and no later.
by 200 bc, the rules for a daughter's marriage seems to have become even more strict.
the religious texts of that time contain strict moral laws that enjoined the father to marry off his daughter before she reaches puberty. sage manu of that age has categorically written in his treatise, manu smriti, that if a girl remains unmarried after reaching the puberty, the father has failed in his duty towards her.
similarly, another sage, parasara, said that the parents or guardians of a girl in who reaches puberty before marriage will definitely go to hell. such rules imposed by the "holy ones" had their effect upon the religious population, and the practice of child marriage was firmly established by 200 bc.
(child marriage in nepal, http://www.cwin.org.np/resources/issues/child_marriage.htm)
the encyclopedia of religion and ethics says:
[it was considered] sinful on the part of the [hindu] father to allow his daughter to attain puberty without being married and the girl herself fell to the condition of a sudra [i.e. low caste], marriage with whom involved degradation on the part of the husband…the smrti of manu fixes the age of husband and wife at 30 and 12 or 24 and 8 respectively; the later work of brhaspati and the didactic portion of the mahabharata give the wife’s age in these cases as 10 and 7 respectively, while yet later texts give 4 to 6 as the lower and 8 as the upper limit. there is abundant evidence that these dates were not merely theoretical.
(encyclopedia of religion and ethics, p.450, http://books.google.com/books?id=inji4fgelpyc&pg=pa523&lpg=pa523&dq =manu+ix+a+girl+should+be+given+in+marriage+before+puberty&source=web &ots=7wp3uyxj9v&sig=hn-o7gg0ya_0qtuwcveujgpqg_y#ppa522,m1)
the encyclopedia of religion and ethics says further:
we find the rule, almost universally valid in the smritis, according to which the nagnika, i.e. a girl going naked and yet immature, is the best (wife).  ....manu shortly afterwards (ix. 94) lays down that a man of thirty years shall marry a girl of twelve, and a man of twenty-four a girl of eight years...in baudhayana  it is 58
stated: "to a virtuous, pure husband the girl should be given while she is still immature; even from an unworthy man she should not be withheld if she has attained womanhood."
the strict injunction regarding marriage before the commencement of puberty gains additional force from the fact that disregard of it is represented as accompanied by evil consequences for the father. while manu is content to characterize the father as blameworthy  who does not give his daughter in marriage at the proper time, it is stated in vasistha: "for fear of the commencement of puberty, let the father give his daughter in marriage while she is still going about naked. for if she remains at home after the marriageable age, sin falls upon the father." 
...observance [of child marriage], at least among the brahmans, became essential and fundamental for orthodox hinduism.
(encyclopedia of religion and ethics, pp.522-523, http://books.google.com/books?id=inji4fgelpyc&pg=pa523&lpg=pa523&dq =manu+ix+a+girl+should+be+given+in+marriage+before+puberty&source=web &ots=7wp3uyxj9v&sig=hn-o7gg0ya_0qtuwcveujgpqg_y#ppa522,m1)