I do remember my first crush except that I did not know that was what it was until more recently. I was eight or nine and it was a girl-crush. I thought that C* was amazing, cute and desperately wanted to be her friend but I was in the wrong social circles / friends-group / clique even at that age.
I also remember my first boy-crush and my first older-man-crush. I never told either of them how I felt but then, in the latter case I expect that it was totally obvious and in the former case I was, yet again, crushing on someone in the popular clique whilst being a geek/nerd/swot/square and bullied non-stop.