I'm 39 years old. I started doing CrossFit when I was 36 and BJJ (Brazilian jiu-jitsu) when I was 37. Before that, I spent years at a fairly standard gym, but I was looking for a change. Currently, a normal week for me is going to the gym about 5 times (sometimes 6, sometimes 4): 2 to 3 days at the standard gym, 1 or 2 days at CrossFit, and 1 day at BJJ. There are a number of potential criticisms of this- "You'll never really progress at BJJ going only once a week," or "You'll miss out on the intentional programming at CrossFit if you don't go more often," or "You're targeting muscle groups so infrequently with random days at a regular gym," among others.
As time goes on, I'm less confident those criticisms are accurate, but even if they are, this more varied routine is something I'm really enjoying. Some weeks, due to work and other factors, I miss going to CrossFit and/or BJJ. My days at the standard gym involve usually a barbell movement initially (squats, front squats, deadlifts, or romanian deadlifts), followed by a variety of movements, 4 or 5 sets for each, not really planned in advance. Each day, I usually do just one and at most two movements for a given muscle group- avoiding the "chest day, arm day," etc. mindset which often leads to diminishing returns on a given day due to "junk volume" for a muscle group as I learned from a great coach.
There's a lot more I could say about CrossFit, but overall, it's the best combination of strength and cardio I've ever found. For BJJ- it was something which was way outside my prior experiences and comfort zone. It also incorporates a lot of mobility and core strength in ways I didn't anticipate.
There can definitely be value in following a more consistent and specific fitness program/routine. But there can also be value in mixing things up. What do you think? What has worked or hasn't worked for you?