Its so much harder to keep a healthy weight as we age. As we age we lose muscle, which burns calories, even at rest. One of the best things we can do as older people is do some resistance training to help maintain muscle. Its said that after 30 years of age we lose 3 to 8 percent of our muscle mass per decade, and this lose increases with age. Keeping muscle through resistance training will help with everyday activities like climbing stairs, walking, balance, lifting things etc.. It also can help balance blood sugar levels, boost mood, increase metabolism, improves heart health, prevents injuries, and also strengthens bones, ligaments, and tendons. The reason older people are more prone to falls, is because of muscle loss that supports their frame, and helps to aid balance. Back injuries are another thing that older people get. The best way to help prevent back injuries is to keep your core strong, mainly your abdominal muscles which support your spine.
As we age we are just not as active, which leads to this lose of muscle. We also just don't feel like doing the things we did when younger. Its even harder for older people to maintain a weight resistance program, but if you force yourself to do it. The benefits from it are many.