From this LA Times article Strength training does more than bulk up muscles:
A growing body of research shows that working out with weights has health benefits beyond simply bulking up one's muscles and strengthening bones. Studies are finding that more lean muscle mass may allow kidney dialysis patients to live longer, give older people better cognitive function, reduce depression, boost good cholesterol, lessen the swelling and discomfort of lymphedema after breast cancer and help lower the risk of diabetes.
"Muscle is our largest metabolically active organ, and that's the backdrop that people usually forget," said Kent Adams, director of the exercise physiology lab at Cal State Monterey Bay. Strengthening the muscles "has a ripple effect throughout the body on things like metabolic syndrome andobesity."
The list of benefits of strength training for any age is long.