Indeed, I've been in the m/m ticklescene since it formed, beginning in the late 80s. I have an excellent reputation for safety, sanity and ability - at least among the now-older folk in the scene. As to your question, you want to alternate and balance tickling and edging. If it seems you can get him dangerously aroused even as he is trying to hold off cumming, especially as that toothbrush helps keep him hysterical, you can mess with his mind. "Bet it would feel so good to let go and cum, hmmm?" You can push him closer and closer while describing how you're going to tickle him insane if he cums. If he ever does go over the edge, I would certainly take advantage of his heightened ticklishness and keep going. 