I think there might be a variety of reasons why you might not partake, many of which might not necessarily have to do with age. For me, I'm still comparatively young I'd imagine but I do consider this hobby high risk and relatively low reward (STD v.s. an hour of pleasure). So I try to limit my indulgences. I also don't do it while in a relationship, for the same reasons of the risks involved and compounding that risk by exposing my gf of that moment to it. Yes, I'm always safe with SPs but there are no guarantees.
But that's just me, others might have a variety of reasons they don't partake...or do it less than they once did.