Wow! I had no idea that there are other's with autism who are like this too! There are times like in structured environments and when talking one-on-one with a person, I don't seem autistic at all. At the most they notice that I'm really smart and knowledgable about things, but that's it. The at other times I can't make eye contact, I rock, flap, make strange facial expressions, speak strangely and in a babyish way, loose speech all together, and then of course meltdowns.
When I am talking to a person who is older than me they always think that I am a lot older than 18, and they don't usually think that there is anything different about me. But if I am with my peers, they seem to instantly know that I am different and they are really puzzled by me. But when I am shutting down or having a mini meltdown (just crying), people think that I am a lot younger and/or mentally handicapped. And then one time when my mom and I went to see Riverdance, I was so excited that I started flapping and rocking, my muscles tightened up, and was grinning with a weird facial expression. That was the first, and the last, time I was really like that in public. We were front row and some of the performers noticed and smiled at me.