There was an interview on TV some time ago with someone far wiser than me who said that the ideal age for a woman is half the mans age plus 7. I think that gives a better (ie legal) result for the 20 year olds and still works for the 40+ group
I'm an old fart of 45 and was going out with a girl of 20 recently. The blokes at work thought it was great but it didn't work.
By midnight most nights I wanted to go to bed (to sleep) and she was just getting ready to go out clubbin!
The end came when I mentioned that I liked a song we were dancing to (I've got the single). She didn't know the song BECAUSE SHE WASN'T BORN WHEN I BOUGHT THE SINGLE.
At this point I realised I HAD to get a GF nearer my age........