The UK National Health Service (NHS) recommends older adults do 20 minutes of moderate aerobic exercise and 10 minutes of muscle-strengthening every day or 150 minutes aerobic and 60 minutes muscle-strengthening every week.
Use the Exercise Timer on this page to time your daily or weekly exercises. It will remember your time between visits.
Moderate aerobic exercise can be achieved by walking fast enough (or doing other exercises) to make you breathe faster than normal.
Muscle strengthening is less obvious. The following NHS videos show you how. Try them all, then decide which ones suit you best. You might want to spend five minutes on two of them each day, or one minute on ten of them, whatever is best for you.
 See http://www.nhs.uk/Livewell/fitness/Pages/physical-activity-guidelines-for-older-adults.aspx The recommendation used here is one of several different regimes the NHS recommends, the others involving more vigorous and shorter daily or weekly exercise. Also it is not easy to find their daily recommendation for muscle strengthening, which is one reason I created this page.
Exercise for Seniors which will quickly remind you of all the exercises.