RP theory is that male SMV peaks at 40. Women "age like milk" vs men "age like wine". This makes some sense as women lose their beauty as they get older while men make gains in personality, experience and career. Why not play the field the longest you can, and then get married at your highest point in SMV?

Some of the friends that got married early have said they regret not playing the field more. And while it might be "optimal" to wait, its kinda the thing where life just happens. You meet a girl you really like, become attached, she seems like a good life partner and you get married. Strategizing doesn't always work.