(2) Men are obligated in procreation (periyya u-reviyya), but not women. When is a man obligated in this mitzva? From the age of seventeen. Once he reaches [the age of] twenty years and has not married, he has transgressed and neglected a positive commandment. However, if he is involved in Torah and engrossed in it, and he fears that if he marries, he will have to busy himself with supporting a wife and thereby come to neglect Torah study, then it is permissible for him to delay [marriage]; for one who is involved in a mitzva is exempt from another mitzva – all the more so regarding Torah study.
(3) One who is in love with Torah and studies it and cleaves into it always, as Ben Azzai did, commits no sin thereby. That is, providing his sexual desire does not get the better of him. If it does, he is required to marry even if he already has children, in order that he not come to thoughts of sin.