In fact, 55 years old is still a good age from another angle. The bones still have considerable strength, and you can do some equipment exercise. Because your father does less exercise, you can still have an obvious physical recovery process when doing exercise. Dumbbells with the right weight are a good choice. Dumbbells can do many actions, but they are also suitable for avoiding lifting dumbbells over the head, squatting down, and landing on the knees.
It should be emphasized that middle-aged and elderly people are lazy. Since you want to exercise, you should supervise your child to form a habit and pay attention to safety. You'd better exercise with your father.