This is a question we get a lot. How much do people in their later years need to exercise to see a difference. The answer is the same for every age group: whatever length of time you can maintain over a period of time.
Physiological benefits of exercise starts to accrue after any amount of training that creates a positive stress on our body's tissues. If we haven't been walking much, then walking for 3 minutes straight can improve our endurance from it's baseline. if we haven't been resistance training, then performing 5 repetitions of squats improves our quad strength etc.
Like most things in life, consistency is the key. So, there is our answer. Ask yourself not how much time you can do on any given day, but how consistent you can be!
Happy moving!
Josh
