I'm 31 and and a black belt and the number one thing I've learned is that too much of anything is bad for you, especially when it comes to grappling, which has wrecked my body more than anything else I've done. I'm relatively young but I've already had 3 hernia surgeries, a scope for a fully torn meniscus, dealt with bursitis in my hip for years plus a bunch of other shit along the way.
These days, I try to incorporate as much variety as possible. On a weekly basis, I like doing Jiu-Jitsu, boxing, Muay Thai, interval training, longer runs, surfing and lifting. I've realized that most of my past injuries came from overtraining in one area and then developing imbalances as a result. I take lots of breaks from grappling too, because I really think that's what has messed up my joints the most. I'm by far healthier and happier than I've ever been in my life, so I'd say it's working. My skills haven't fallen off either. At any moment, I'm only a solid month or so of training away from being right back on top of my game. I'll take that over being constantly injured but slightly sharper on the mat on a day to day basis.
Of course, that's only what I think makes sense for me now. When I was younger and had no injuries, I had to grind daily to build my skillset. Once you're passed the point of diminishing returns though, you need to start picking and choosing more. I only train with a specific purpose in mind now and I pick my battles. I have zero shame in asking a lower belt for a lighter roll when I'm trying to be more careful. I wish I'd done more of that in the past.