The biggest reason I think, is that most older men want to go 10-15 years younger. Not a little bit younger, they want to go a lot younger....and thus there are less men in an older age group.
There's more single men in general I believe until you get up into the older age brackets when men start croaking. The Census Bureau tracks all that stuff, something like 35 pct of men have never married as opposed to 28 pct of women.