You get ancillary knocks and bumps in BJJ (catching a knee in side mount, or screwing up a takedown and bonking yourself), and while they're not that bad, after a lifetime of playing for fun, it was time to stop.
Running and basketball I had to quit because of impact on my body overall, though not so much my head. Wakeboarding I quit b/c of a torn ACL and minor concussions in my 20s. Skateboarding is obvious lol. Surfing doesn't have very much impact, but in big waves there is a whole other set of risks.
Anyway, I was just a bit surprised by your comment b/c out of all the sports I've done, BJJ seemed like the one I could do for a very long time just by sticking with people I know and trust.
It's definitely safe if it's the first thing you've ever done, as the lower levels of bumps are new, but if you've done similar things for a long time, you definitely feel the accumulation in your brain and joints. It's super dumb because it's literally my favorite thing in the world, but I want to be a sharp tack when I'm old and I couldn't sustain it.
At this point in my 40s I've got nothing to prove. If someone comes at me spastic, I tap and move on. The algorithmic/thinking side is really a big draw for me (and it seems others). Over half the people in one of my typical classes are programmers. Time will tell if I can do it in a way that allows for longevity - I certainly hope so. Good luck to you!