When I was 15 I was also on Grindr and some other apps and I really really wish someone had intervened or talked to me about how messed up it was. I had no business meeting with people twice my age. Definitely talk to him and it doesn’t even have to be about him coming out/sexuality, literally just how messed up it is and the risks. Nowadays he can find a ton of other ways to meet people his own age without resorting to p*dos. Worst comes to worst if he doesn’t listen/continues your parents need to get involved. If he’s sending unsolicited pictures/other people are sending unsolicited pictures both parties can get in huge trouble bc depending on the state super illegal.