apparently one fairly sure sign is if your parents refer to you having been odd, different, etc. I knew that i always pushed people away, my mother included, when they tried to hold me cos my mother told me many times, but when i told them recently about thinking i'm aspergers, thus on Autistic spectrum , my mother said another thing they'd noticed was how i needed lots of notice before doing something new, and they learned to prepare me far in advance, telling me about it etc, AND another thing , that it seemed like i simply didn't seem to be able to see anything from other peoples point of view, including the effect i was producing on people.
etc etc
Point is AS is from birth, or within first two/three years , and so signs from then are good indication.
However an aspie parent might not notice this kind of thing in their child. For example it wasn't until my mother said my sons language skills ( at 5 years age) were really poor that i began to realise he really did have some sort of genuine problem, and not until discovered my own AS that realised his pervasive development difficulties ( at age 8 !).
So...
PS: you're a guy so it might not be relevant to you but there is also some theory now that in females AS might express differently because of the female empathising bias, or social pressures, whatever, meaning female AS might become almost super good at bursts of hi-power socialising but it would be a strain ( on energy and intelligence) because would all be worked out from complex and deliberate copying and mimicking. This might make AS in women less visible until extra stresses are put on the person, at puberty, or independence at age 18, whatever.
