Can you adopt a 18 year old?

Well, for adoption, you have to get official papers sent to the court and all and I'm pretty sure there's a hearing (I'm not a lawyer) so I think it's up to a judge. I remember when I got adopted, there wasn't a formal hearing I don't think (I was 9, I'm 18 now so it's a bit fuzzy haha) but the judge talked to me and talked to my parents and asked me if I wanted to be adopted and probably did legal searches and stuff on my (now) father. So, if the judge deems you to be a fit parent and the 17 year old is okay with the adoption, then they should agree to everything. I don't really see the point, it's just a year until they're 18 and legally an adult. Maybe you want to do it for insurance purposes? I don't know. Just a guess.