There are several benefits of staying fit through exercise and it is an established fact. As people become old it may become more of a challenge to stay fit and as their muscles weaken indulging in simple exercises could be difficult.
However, seniors do not need vigorous exercise to stay fit. They can do extremely simple exercises which would still help them in living a healthy life.
For seniors more than doing the exercise, how often they do it matters to a great extent. A senior should aim at a fitness program that advices them to do exercise at least twice a week. It may be simple exercises which involve meditation, yoga or walking, depending on their physical abilities. Unexercised muscles tend to become dormant as you age and that is why it even more important to keep them in shape. A physically active person has much less to worry about health wise. Frequency of exercise should be consistent more than the amount of exercise.
The intensity and the duration of the exercise are secondary for seniors. Usually seniors are advised to take short walks within the yard of the house or simple leg and hand movements. These simple movements improve the blood circulation and also strengthen the muscles. Stretching is a simple and good exercise for old people. It is also easy to do and does not need muscular effort. Even few minutes of exercise everyday has huge benefits health wise and you should allow some time for warm up while exercising.