High Intensity Interval Training (HIIT)
If you want to do the least amount of exercise with the most benefit in terms of metabolism and weight loss do HIIT (High Intensity Interval Training).
All you need is 10 minutes every other day. The idea is to work out to exhaustion. One minute on and one minute off for 10 minutes.
The type of exercise is a lot of jumping up and down motion. Things like jumping jacks and squat thrusts.
Always exercise within your limits in terms of age and safety and injury awareness. In other words, use your head.
Here is a video that gives you an idea of the kinds of exercises that are available to you.
Exercising like this for only 10 minutes every other day keeps your metabolism running higher all day long.
Here is another exercise video on HIIT.