I'm in my mid/late 20s, but I always get mistaken for being anywhere from 12-16. I'm female, and I do not consider it a good trait at all. It makes it so much harder to do a lot of things because people assume you're a teenager. It makes it even harder to make friends or have people respect you, because people take one look at you and see a teenager, so they wouldn't even consider that you could be their friend or whatever. And all the awkward questions you get--how old are you, what school do you go to, etc. When you answer, they act all shocked. There are many other bad things about it, too, and only a few good ones that I can think of, with possibly more good traits as you get older and start at least looking like an adult. My dad also looks very young for his age, and was recently mistaken for being my mom's son, which was embarrassing for them both. He has a lot of ASD traits, too.