I think it's that males should marry women 10 or more years their junior. I also think women should shoot for this too(older men). I don't think it's an accident that for much of history, that was the norm. The benefits are myriad.
1)Odds are that generally, a women 10 years jr will remain competitively attractive to their hubby for the duration(with obvious exceptions).
2)Men tend to be less established younger and so, women benefit from marrying a guy who is more "set".
3)Whether people like it or not, men are generally considered attractive BY WOMEN at later ages than is the reverse. Women get pissed about this fact as if it's some male conspiracy but men aren't the ones deciciding that it's typically attractive to 25 year old women. Women are doing that. And, I don't think that's an accident either. I mean hell, VERY few 35 year old women even find someone like Justin Bieber interesting. Meanwhile, tons of 25 year old women ogle the frick out of 45 year old actors.
Just look at this site. Post a pic of 40+ actresses that actually ARE attractive and many young guys in here go....."meh". The reverse aint true!!