Yes, exercises that use only body weight can certainly be used to build and maintain strength. However, you should also consider other benefits of increasing and maintaining flexibility and balance just using your body weight for stretching and calisthenics. I have been using a home-based approach like this for the last 5 years and I am very pleased with the results. Not only am I stronger but I can see the difference. I like not having to go to the gym as it saves time and money. I do this for about 20 minutes each day and two days a week I supplement my program with another 15 minutes using 10, 15 and 25 pound dumbells. I find the dumbells help me especially with upper body strength in my arms, shoulders and chest.