I don't think it's all that odd for Men to marry younger women; there's historical precedent dating back hundreds of years actually.
In my case it just worked out that way. I wasn't interested in marriage or kids when I was in my 20's. I liked being single. I liked going to the gym, riding Motocross, playing my guitar loud, having a 110" projector in my bedroom (WAF factor NO!) having a dedicated game room to link xboxes over LAN, playing PC games till sun came up, going out at night drinking with my friends, chasing different women, and not having to answer to someone or worry about someone else in my decision making. Around the age of 31 my outlook changed, I think I just matured and actually got my fill of all that "boy" stuff. My wife had a big part of that too.
Things just kind of naturally developed but I can say honestly I never though too much about marriage until I met my wife. She was 24 when I met her, I was 31.
I think generally speaking that 28-33 year old men have a natural attraction towards slightly younger girls 22-27 because women are more mature and ready for marriage and kids sooner and there's often a big difference with men in early 30's in terms of income, stability, maturity etc... Girls just like that stuff. Guys OTOH like the younger and physically fit women because of simple physical attraction. I was doing a lot of internet dating before I met my wife and I had dated a few older girls (couple years older, nothing crazy ) but they seemed like old ladies to me. I dated a 34 year old then a 24 year old back to back, I remember realizing that I just liked the younger girls more because they were more fun. This of coarse isn't always true but I think it's true enough to explain why a lot of guys date younger girls (and sometimes marry) and also why a lot of younger girls like to date older men (and also marry). Marriage has more to do with finding the right person than ages do of coarse, but attraction and getting a quality relationship started are the first step.