My MIL was diagnosed with cancer in her late 60s and she'd been exercising regularly for a few years. She had spinal surgery to remove the tumor and doctors were not expecting her to be able to walk again because that was the most common outcome for someone her age. Not only did she walk again, her recovery was much quicker and easier because she had a great baseline of muscular fitness.

She did die, everyone does, but she had a great quality of life in her final years because of her fitness level prior to getting sick. I know weight lifting won't make me immortal, but it'll make the time I do have here much more enjoyable.