15 or 16 year olds passing as 18 year olds. Yes, that can happen, but that’s where I’m saying the adults (especially when you’re talking about guys in their 30’s or 40’s or older, not just college aged guys) have to take no chances. If she even looks like she might be underaged, steer clear (and if she’s young enough to actually BE underaged, she’s young enough to look like she might be).
Everyone knows that ID’s are not reliable ways to check age, so I think it’s disingenuous to suggest that if a guy relies solely on that for a girl he doesn’t know, that he’s doing everything he can. He’s going through the motions, but he’s not really trying.