Boyfriend wants a blow-job but I don't want too

Okay so don't make fun of me or anything but I just turned 13 and my boyfriend who is 14 wants a blow job and i just don't want to. We are kinda advance sexual for our ages we have given each other hand jobs but not sex i wouldn't do that. He kinda ate me out one day but kinda not. I just don't know how to tell him that I don't want to give him a blow job because he asked me for one so please help me.