i have a friend who is a total predatory douchebag who had a 16-17 year old girlfriend in his mid 20s and on her 18th birthday while fucking her, he made her keep repeatedly scream "'i'm seventeen".
she told us this after their breakup (she got with someone edging 30 at 19), he has zero sense of humour about his desperate need to get his end away.
his current girlfriend is an art grad who has a personality pulled straight from a nursery rhyme.
the only time i've gotten into a bar underage was one of those 'knew a dude who knew a dude' type of situations, and that was maybe twice. in the age of blacklights and chip scanners fake id's seem futile at all but the dingiest joints.
when i was coming up, they were super lax. there was this one dive bar which doled out double gins to us for a quid as long as we never left the back room, and the local clubs seemed to have some arbitrary system where they'd ID you maybe once a month. if there was a big group of you, you knew you wouldn't all make it. basically our generation's world war one.