What things do seniors need to think about before beginning a new exercise regime?
The most important thing is that you are aware of your personal limitations, including places in your body which can get tight, places which are weak, and areas which are prone to injury.
If you have a debilitating injury, such as arthritis, then be careful about what you do. You also need to be aware of the fact that older people can suffer from low blood pressure.
If you do, then be careful or try and avoid too much overhead exercises.