If you want to be healthy and fit your whole life, forget six pack abs, get a strong back. Your back is so important, especially if you’re over 40.
At almost 70 years young, I have found these exercises work well for me:
Since my genetic heart problem was diagnosed about two years ago, I keep my bodyweight and weighted exercises at low reps. Usually I do 1-3 reps per set, and it has helped me a lot. I do axle deadlifts and pullups/chinups regularly.
The only volume work I do is my Mace Fit® training. Mace and club workouts really hit your back muscles.
You can read more about my training here