Walking is one of the simplest and most effective activities for older people. It builds leg strength and stamina, is free, and can be done at your own pace.
If you are building up from very little, start with short walks on flat ground, perhaps to the end of the road and back, and gradually go further. Walking with a friend or joining a local walking group can make it more enjoyable and easier to keep up. Many areas have health walks designed for people who are less active or recovering from illness.
Indoors, simply walking more around the home helps, as does getting up regularly rather than sitting for long periods. Gentle housework and gardening count as activity too.
Other good options include swimming and water-based exercise, which take the weight off painful joints, and gentle classes such as seated yoga or tai chi, which are particularly good for balance. Dancing, bowls and gardening all count, and choosing something you enjoy is the best way to keep it up.