The changes we feel from getting older should be getting your attention. Feeling more stiff, feeling a bit breathless with some exertions, noticing your body move with less strength and balance, a sense of weaker word recall and memory.
Flexibility, strength, aerobic capacity, mental sharpness. Start with this. We can't change all at once but we can change.
What does it look like when I pick one of these parts of myself to work with?
If it's aerobic capacity, you can start with faster than normal walking or riding a stationary bike with a little bit of resistance dialed in.
The key is to do the same exercise at least 2-4 times a week. And try to make it routine. If you start with faster waling, pick a defined route and time yourself. If it takes you 20 minutes, do the same route again and again at the same speed, in 20 minutes or less, but not more. Keep it the same and keep repeatig 2-4 times a week. You've picked something to begin. After 3 weeks, add something else.
If you're adding flexibility, you should learn a simple approach from one-on-one training with a Chiropractor or PT. Learning this way is important to maximize the value of your stretching. But you are not stretching to be virtuous. You want to feel different, better, when you finish 20 minutes of stretching. Keep repeating the same stretches 2-4 times a week. After 3 weeks, add something else.
You're now working every week on aerobic fitness and flexibility. You can add strength training. A very simple approach is to sit in a chair with both arms outstretched in front of you. 2-4 times a week, using just your legs, stand up from sitting and then sit down again. Do this 5 times in a row. Rest briefly. Again, with both arms straight out in front of you, standup and sit 5 times without using your arms to help you up or down. Repeat this for one more set of 5. You have now done this 15 times.
After 3 weeks, add work on mental clarity. The simplest way is to listen to a podcast of something that interests youbut it is not simple. It can be in any field but it should be a mental stretch to understand what you're listening to. A good example of mind growing material are the health related interviews presented by Peter Attia, MD. Peter interviews other tip physicians and scientists who share their insights on what they're studying. (https://peterattiamd.com/) Try to listen 2 times a week.
You are now using the approach of 'pick something, add something' to grow in the opposite direction of againg. You can add more repetitions or intensity to any of these areas. Just keep what you already have and add something!