As a 13 year old 9th grader with a crush on a 16 year old 10th grader, do I have a chance? (he has a late b-day and did 8th grade twice, I skipped 6th)

I think you definitely have a chance with this person. If you are in the same school you can take your chance and ask him about something, ask for his help with your studies, anything school related. Just act naturally, be yourself, try not to worry and panic if you talk to him. If you have common friends you can organize something where he could show up, or maybe you have common hobbies or interests you can use it as well. Try to spend more time with him, ask his opinion, his help, maybe offer your help with something.