It isn't about whether or not two 20 year olds are or should be having sex. It boils down to a respect issue. Your son should have made sure it was ok with you and your wife first. I'm sure that by age 20 they're probably both having sex, with each other or with other people. But they don't need to be doing it under your roof. A parent doesn't want to hear their kids having sex any more than a kid wants to hear their parent having sex.

This is the whole reason that cheap motels were invented.

__________________
Jonathan

2011 Mazda2
2000 E320 4Matic Wagon
1994 C280 (retired)