GEN143 It is a positive commandment to marry a wife in order to be fruitful and multiply (have children) as Scripture states, And God said to them: Be fruitful and multiply [this verse]. One's intention should be the continuation of the human species. When a man is eighteen, he becomes subject to the duty of begetting children; and if he passes the age of twenty without having married, he thus transgresses and disobeys this positive commandment. If he is occupied in Torah study and he fears that the problem of earning a livelihood will interfere, he is permitted to delay – but in any event not beyond the age of twenty-five. CCCBM 59