Yes, some seniors can be frail and have low energy reserves but most of us will respond well to moderate sessions of weight training. Numerous studies have shown that strength training for seniors and other exercises for seniors done regularly not only builds up bone and muscle but counteracts the weakness and frailty that usually comes with aging.
The good news here is that muscle patterning improves within days of starting a weight-lifting program, even without any increase in muscle mass. This explains the 113% increase in strength experienced by the residents of the nursing home in Boston in the previously cited study. In a different study that specifically investigated this phenomenon, 67- to 81-year-old men lifted weights for six weeks while hooked up to electrodes that measured their nerve and muscle patterning (an electromyogram machine). The results showed that the men experienced a 25% increase in the patterning of the muscle along with a 35% increase in strength, all without significant increases in size.
Importantly, strength isn't just a function of mass. It's also a function of something called "neurological patterning." In layman's terms, patterning is when the brain sends electrical signals via the nervous system to muscles to make them contract. For example, when you think about walking down the street, bending over to pick something up, or any other movement for that matter, the brain first processes the thought and figures out what muscles are needed to make the move and then sends the signal over the nerves to the particular muscles that are necessary for the movement. The muscles move (and so do you) once the signal reaches them. (See "How muscles work" for more detail.)
Get motivation and find support by joining an accountability group and surround yourself with people working towards similar goals. These groups are designed to increase your performance, measure your progress, keep you engaged, and allow you to express your thoughts and feelings. Search for groups through your social media accounts. Discover forums (like this one!) where you can share about your journey and receive virtual support from others going through the same experience. If you're feeling courageous, start one of your own!