Ds1 is 20, far too old for me to be thinking about this for the first time, I suppose, but he was 18yo when he was last able to socialise. It feels like he's gone from being a child to a man without any transition period iyswim.
Anyway, he's been out a lot in the last few weeks so I knew something had changed and he's now told me about his 18yo girlfriend. 
I'm really pleased that young people can live a bit again and we've had a conversation about respect and staying safe etc (which again he's too old for and it's not the first time, but..). I've told him he can invite her round any time. He's been to her house and met her parents (has brought cake home made by her mother, so I guess they don't hate him).
Anyway, If they're not already I imagine there'll be some sex. I do think they should have somewhere safe and comfortable to go, but I don't want to hear it in the room next door to mine!
What do young adults , living at home, do about sex? My parents would never have allowed us in my bedroom when I was that age which is one of the reasons I married very young