Is it okay to avoid an autistic kid at my school?
Why would you avoid this person?
I've heard some awful stories about him
I understand you're uncomfortable because of what you heard, but you don't really know this person. It's best to make your own judgements. A person isn't bad just because they have a disability.
It's not my fault that he is autistic.
Their condition could be overblown and people are making outlandish rumors about them. See how they really act and get to know them before you completely ignore them.