What is the preferrable age for a boy to get married?

1. Nabi (Sallallaahu Alayhi Wasallam) is reported to have said, 'He who has the ability to marry, should do so.' (Mishkaat).
There is no specific age or time by rule at which one should marry, however, from the teachings of Nabi (Sallallaahu Alayhi Wasallam) we are taught that one should not delay. After a person matures and once he becomes responsible and it is easy for the necessary arrangements to be made, he should immediately get married. This may vary according to difficult individuals. Generally, one average in our times, approximately 20 - 21 should be a good age.
2. From the outset, we must understand that Talaaq is most hatred in the court of Allah Ta'ala. This earns the anger of Allah Ta'ala. When a dispute between both spouses occur, all sorts of effort for reconciliation should be thoroughly looked into. Nevertheless, going for Jihaad is not compulsory upon every single individual at present times whilst to fulfil the rights of our wives is compulsory. It will, therefore, not be permissible to give the wife Talaq merely becase she stops the husband from Jihaad. Instead, there should be understanding between husband and wife. The husband should make an effort to inculcate good qualities in his wife, making her understand Jihaad and all other aspects of Deen so that when Jihaad does become compulsory, she will encourage him to go forward.

and Allah Ta'ala Knows Best

Mufti Ebrahim Desai