My partner is 16 yrs. older and we've been together for past 14 yrs. I am 48.
Since he is quite fit ..meaning cycling an average of 10,000 kms. annually and when I meet his male friends, many who are cyclists (and reasonably fit) in his age bracket or younger, I currently have a warped sense of what less fit men look like/should look like at MY age.
When I meet men my age occasionally, I am abit surprised how some just look far more unfit than my partner. But this is more the norm.
Since I do work in a male-dominant workplace right now, meaning over 150 people, of which only 25% are female, it is something to guess/compare men's real ages and how they have weathered the years.
There's probably a good proportion of guys at work, who are younger, meaning mid-30's to mid-40's.
If I were to be interested in someone younger, probably no younger than 10 years.