That young, you guys don’t have anything really invested in the relationship. Trust me, this gets a lot more difficult as you get older.
The way I’d do it if I were you is I’d start declining invitations to go out or hang out. Then when he asks why just tell him “you need space.” People who’ve been around the block a few times knows that’s code for breaking up and will just accommodate your request.
But he probably won’t and will want to know what you mean. So just tell him you want to be alone for awhile. If he asks whether you guys are breaking up, I’d try to hide my delight and just say with as much sincere sadness as you can muster, “I guess we are.”
13–17 is too big an age differential anyway. As soon as he turns 18 you’d have to break up regardless. You can bring that up too if you need an excuse.