Getting married is not like picking up a loaf of bread. It can take a while to make a shidduch.
That means one must start looking and be ready at an early enough age to be able to married by the halachicly necessary age. If starting at 23 means there is a good chance one wont be married by 24, obviously folks need to start earlier by however many years necessary to be compliant with the Shulchan Aruch or the latter shittos if engaged in full time Torah study.