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It says the man may marry earlier than 24. Clearly, Manu Smriti is not specifying a hard minimum age. and based on the previous 2 lines of this verse, it may be inferred (assumption, could be right or wrong) that the corresponding age of the girl can be lower. There is no verse that sets athe hard lower-bound at 8 years. Case in point - there is a similar Manu Smriti verse about the age of upanayana for boys :

It says the man may marry earlier than 24. Clearly, Manu Smriti is not specifying a hard minimum age. and based on the previous 2 lines of this verse, it may be inferred (assumption, could be right or wrong) that the corresponding age of the girl can be lower. There is no verse that sets a hard lower-bound. Case in point - there is a similar Manu Smriti verse about the age of upanayana for boys :

It says the man may marry earlier than 24. Clearly, Manu Smriti is not specifying a hard minimum age. and based on the previous 2 lines of this verse, it may be inferred (assumption, could be right or wrong) that the corresponding age of the girl can be lower. There is no verse that sets the hard lower-bound at 8 years. Case in point - there is a similar Manu Smriti verse about the age of upanayana for boys :

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First, your question title contains an underlying assumption - that 'he had no intention of leading married life before he got married'.

The same wikipedia article you linked states :

Ramakrishna's mother and his elder brother Rameswar decided to get Ramakrishna married, thinking that marriage would be a good steadying influence upon him—by forcing him to accept responsibility and to keep his attention on normal affairs rather than his spiritual practices and visions

in 1856, Ramakrishna took his place as the priest of the Kali temple

Ramakrishna himself mentioned that they could find the bride at the house of Ramchandra Mukherjee in Jayrambati

..marriage was duly solemnised in 1859

In 1861..the Bhairavi initiated Ramakrishna into Tantra.

In 1864, Ramakrishna practised vātsalya bhāva under a Vaishnava guru

In 1865, Ramakrishna was initiated into sannyasa

After the marriage, Sarada stayed at Jayrambati and joined Ramakrishna in Dakshineswar at the age of 18.

Yes, he was a priest before marriage. It is quite possible that he was not inclined towards married life, but on the behest of his mother & brother, decided to accept it. It would be another 9-13 years before his wife joined him. In the 6 years between his marriage-date and sanyasa-date, he had undertaken severe spiritual practices, which could have firmed his resolve to sanyasa. Hence, his mind could have changed after marriage.

Then, what about the plight of the wife ? It is accepted in shastras to take sanyasa if mother accepts it (during brahmacharya) and wife accepts it (during gruhastashrama). In this case, we don't know whether he consulted his wife or not. But if the wife does not raise any issue after coming to know about it, there is no problem. There is also the famous history of a sanyasi returning to married life at the behest of his guru who had met the wife praying for progeny (can add source when I find it). In this case, the same wikipedia article says :

Ramakrishna became a very influential figure in Sarada's life, and she became a strong follower of his teachings

It is also very well known that she undertook teaching his philosophy after his passing, so there is no evidence that she was against his decision.


Second, your 2nd question also contains an assumption/opinion, disguised as scripture ('putting words in mouth') that '5 years seems too low even according to Manusmṛiti'

Short note - The intent of child marriage (for a girl) is the same as that of child upanayana (for a boy) - both used to happen around age 7. The boy surrenders to a guru, and the girl to her husband, before kama (lust) enters the heart around puberty. But the difference is that, while the boy immediately leaves to gurukul to live under Guru's tutelage, the girl usually does not join her husband's home until she comes of age at menarche (Source - Hindu Dharma)

The same Manusmriti verse you quoted regarding the age of marriage says:

in the event of his duties suffering, he may do it sooner

It says the man may marry earlier than 24. Clearly, Manu Smriti is not specifying a hard minimum age. and based on the previous 2 lines of this verse, it may be inferred (assumption, could be right or wrong) that the corresponding age of the girl can be lower. There is no verse that sets a hard lower-bound. Case in point - there is a similar Manu Smriti verse about the age of upanayana for boys :

In the eighth year after conception, one should perform the initiation (upanayana) of a Brahmana, in the eleventh after conception (that) of a Kshatriya, but in the twelfth that of a Vaisya.

(The initiation) of a Brahmana who desires proficiency in sacred learning should take place in the fifth (year after conception), (that) of a Kshatriya who wishes to become powerful in the sixth, (and that) of a Vaisya who longs for (success in his) business in the eighth.

Normally, upanayana is done at age 7. But Advanced souls can have the samskaras done earlier. Adi Shankara had upanayana at age 5. Ramakrishna was well-known for his mystic visions from quite an early age. It is possible he knew in advance about his would-be-wife's spiritual characteristics. Even if not, shastras do not forbid early upanayana (or by corollary, marriage).