Search terms: homeless/runaway/amnesia(c)/missing, teen/minor, police, child protective services, 16/17/18, and about a bazillion variations and combinations thereof--since I'm looking at cases involving minors, actual details are pretty hard to come by... and googling "unidentified teen" was a bad move since I just found a bunch of awful murder stories :(
I sorta wrote myself into a corner here. So there's this character who has absolutely no paper trail--no birth certificate or SSN, no ID/driver's license, no medical records, school transcripts, nada. He has no family, no friends. (If it matters, the reason there's absolutely no trace of him existing is because he's from an ~*alternate dimension*~, and was never born in the universe he's stuck in--he can't even steal an alternate dimension doppelganger's identity!)
He winds up attracting the attention of the police--hospitalized for possible assault or arrested for a petty crime or somesuch, basically something that ends up not being a big deal. The problem is his age. Now, he looks young--but ambiguously so. As in, most people would place him between 14-16 years old, but he swears up and down that he is 18, which--you know, the believability of that really depends on the person, because there's not necessarily a lot of difference physically between many 16-year-olds and 18-year-olds.
So the police (or CPS at this point) strongly suspect that he is a minor and are trying to figure out who he is and where his parents are, but when they ask him where he lives, he becomes extremely evasive. He won't tell them who his parents are or where they live ("I don't have to tell you that, I'm an adult!") and keeps changing his story around. First he's staying "with relatives," then "with friends," but he's unable to provide a phone number or address for any of them. All of this is pretty suspicious (like, "really kid? You just barfed out a random, obviously fake name and don't have this mysterious person's PHONE NUMBER?") and it looks, for all intents and purposes, like he's a homeless runaway.
This is what I'm wondering: do you feel the police would be more likely to ascribe to the "if it looks like a duck and quacks like a duck" philosophy and assume he's a minor (and presumably involve CPS), or take him at his word that he's a legal adult? Do they keep him in custody while they try to locate any relatives or evidence of his identity? What happens when they can't find any?