Yeah, the question here is what's the average avian's lifespan. For example Strix in the Pathfinder universe live 40-60 years, so that would put Rin past her twenties in human age.
You'd be surprised how more realistic it suddenly seems after a brief tour of Twitter... plenty of people cheering for the death of "lesser beings" going on over there.
It's actually the recurring romantic trope as a whole being referenced, which has actually been a topic of debate in the past, with some strenuously insisting there's no way they exist in real life, and others more pragmatically pointing out a sociable gyaru would be nice to just about everyone...