The Gemara in Kiddushin says the maximum age for marriage is 20. The Shulchan Aruch in EH says a person should be beaten if he doesn’t get married by then. Beis Din can force Reuven to marry Dina if they are refusing to marry by the age.
Some shittos (Maharshal) hold that if he’s learning Torah full-time then he must get married by 24.