I'm male, very late 30s and just starting something with a 19 year old.
I know not all men are the same, but I honestly believe a very large proportion of men my age or older would love to have a 19/20 year old.
For me and the girl/woman I'm starting with, it is what it is, we've been honest with each other about that. It's early days but I have no interest in settling down with her or having kids (been there done that, enjoyed it, but not doing it again). I love the prospect of spending time with her, and yes having incredible sex with her. She gives my ego a huge boost, we both know that, and she makes me feel alive like I've never felt before. She's hugely submissive so really enjoys the effect she has on me and she loves knowing she can have me. Sexually, I'm so much more open minded and assured now, then when I was that age.
I don't think either of us is exploiting the other as we've been totally honest about what it is.
And yes, if/when I tell any friends about her they'll be impressed and envious. They wouldn't want to end their relationships for a much younger woman, but if they were available they'd leap at the chance.
Oh, and to the women saying their husbands find it weird, some might do, but I guarantee some are just saying it. There are a lot of older men who'd love to have sex with a 19 year old.
Where is it going? I don't know, but we'll enjoy it while it lasts and hope it doesn't overrun its course. I don't want to spoil her chances of finding someone to settle down and start a family with. She has time for that, I would encourage her and would absolutely stand aside.