I'm well over 40 and to be completely honest, sex has been getting better every year for many years now.
I only fear STD's and it's a constant worry. Not that I'm all that promiscuous but if my sex partners aren't as honest as I hope they are we could both/all end up with an STD from their encounters.
Everybody thinks they're being careful and are in closed end relationships but often we find out it's been blind luck that we didn't get an STD as the truth is outed.... sigh