Well, I can't pinpoint a moment when I knew I was different.
But I'll try....
I guess on a nonverbal level I knew I was different in kindergarten because I'd play by myself a lot as evidenced in photos and videos.
However, my family never made me feel different and there were communication, which helped lessen the feeling of isolation.
And I went to schools for the deaf which I never knew I was different because I was among with others in same boat. It would be only outside school when I realize how different we are.