At 72 age what Exercise to keep fit should be done?
Fitness can mean a few things. Strength alone, speed, explosive ability, endurance, cardiovascular health, overall health, etc.
Your definition of fitness will dictate which type of exercise you should do.
I was very active in sports and games in my younger days. I admire the most among the the past athletes, two people. Jesse Owen and Carl Lewis. To win 4 golds in a single Olympics in track and field is very extraordinary. They have both speed and explosive power but not strength and endurance.
The event that impresses me the most is the Decathlon. It combines all the physical needs in the various events into one. The perfect all round athlete. Speed, as in sprints, explosive power as in the jumps, explosive strength as in the throws and endurance as in the mile..
So my exercises nowadays are for strength alone, then explosive type of strength, (both within my physical needs), cardiac capacity improvement through indoor cycling and walking and stair climbing endurance. The speed part is not necessary for fitness.
The strength part is exercising the lower body and the upper body pulling and pushing groups of muscles. To regain your lost strength, not for muscle size.
Explosive strength is by doing plyometrics.
Cardiovascular health is through any endurance type of exercise. BUT walking alone will not reach the level required for optimum improvement. Walk to improve your walking endurance, not for cardiovascular health. You get lower benefits than other more stressful endurance exercises.
The above is very easy to write about, but believe me, it will take many months to achieve a decent level of physical and cardiovascular fitness. Your body and muscles will be complaining once in a while.
Start your fitness journey with the cardiovascular part first by walking for 1 or 2 months. You must reach at least 4 mph for 30 minutes. Then you improve further with maybe running, cycling, swimming. Anything that makes your heart rate level go higher than walking can.
Once the heart is able to take additional stress, you can do whatever type of exercise you prefer. Go for strength improvement with body weight exercises. Then plyometrics for agility (power) and balance.
The above will give you a well balanced and rounded physical body. BUT you have to really work hard. That is why the need to do the cardiovascular part first.