Basketball after 40

Hello everyone. I’m 49 and recently got back into playing after a long layoff. I play with guys all 30 or younger. I hold my own offensively because I’m a good shooter, but defensively I’m really bad trying to guard these guys. All are decent to really good and played high school or college ball. I try giving space or crowding and neither works without fouling. It’s frustrating being the weak leak because I can’t guard. Any tips for me? LOL