According to the NHS- Adults aged 65 or older who are generally fit and have no health conditions that limit their mobility should try to be active daily and should do:

• at least 150 minutes of moderate aerobic activity such as cycling or walking every week, and 
• strength exercises on two or more days a week that work all the major muscles (legs, hips, back, abdomen, chest, shoulders and arms)      

or

• 75 minutes of vigorous aerobic activity such as running or a game of singles tennis every week, and
• strength exercises on two or more days a week that work all the major muscles (legs, hips, back, abdomen, chest, shoulders and arms)

or

• a mix of moderate and vigorous aerobic activity every week. For example, two 30-minute runs plus 30 minutes of brisk walking equates to 150 minutes of moderate aerobic activity, and
• strength exercises on two or more days a week that work all the major muscles (legs, hips, back, abdomen, chest, shoulders and arms)

A rule of thumb is that one minute of vigorous activity provides the same health benefits as two minutes of moderate activity