@MNHQ is all 9f MN AIBU now? Why is the AIBU vote facility enabled on a post under teenagers?
wantmysmileback you switched on a vote function to allow people to vote whether or not you are being unreasonable, which is why a poster told you YABU...
As someone pointed out his FB age may have been set when he joined Facebook age 12 and lied because the minimum age is 13.
As a parent I wouldn't be best pleased at my nearly 17 year old DD dating a just turned 21 year old.
I do however know enough young people to know that many just turned 21 year old men are more boy than man, it does depend a bit on the individual.
Your reported conversations with your DD were very manipulative - vanishingly few 16 year olds would have told you their boyfriend was 21 if you said 20 was the oldest you'd accept... You set her up, pretty much.
I'm in my mid 40s but still remember being that age and early 20s was the attractive age..
As a parent it's normal to want your DD not to date anyone older, as a teen it's fairly common to want something different.
It depends completely on the individual - is he respectful, on her level, do they have fun together or is he influencing or manipulating or pressuring her?
I'd keep the pair of them close and encourage them to hang out at yours so you can keep an eye.
Don't ban her from seeing him or she'll get a Juliet complex and you don't want star crossed lovers on your hands...