1,573. Who is Obligated to Marry and Who is Exempt
Hilchos Ishus 15:2
The obligation to procreate is incumbent on a man but not on his wife. A man becomes obligated in this mitzvah at age 17. If he reaches the age of 20 and has not yet married, he is considered to have neglected the observance of a Torah obligation. However, if he is occupied with Torah study and hesitant to marry out of concern that his need to earn a living will keep him from his studies, then he may delay marrying. This is because a person who is occupied with one mitzvah is exempt from performing another mitzvah. This principle certainly applies to Torah study.
Hilchos Ishus 15:3
If a person’s soul constantly yearns for Torah like Ben Azzai's did and he clings to it all through his life to the extent that he never marries, he is not considered to have neglected the mitzvah to procreate so long as the natural urges of a man do not overcome him. However, if his natural urges overcome him, then he must marry even if he has already has children in order to prevent him from having sinful thoughts.