assuming a moderately active lifestyle (e.g. an hour of brisk walking a day), we're skeptical that exercise has any significant advantage, if any, compared to improved nutrition and non-exercise lifestyle changes (more and better quality sleep, better friendships, etc.).
that being said, exercise certainly isn't bad.
If you stop to consider what's going on, it makes a lot of sense. Your body is adaptive. This includes bones as well as muscles. In the same way that you need to add muscle mass in order to lift progressively heavier weight, your bones, too, need to become stronger to support lifting heavier weight. They do this by becoming denser.
If it doesn't raise your heart rate to at least 100+, it's nearly useless as an exercise. Sure, you'll burn slightly more calories than sitting at a desk, but the benefits are nowhere near actual exercise.
> more and better quality sleep, better friendships, etc.
Sleep quality generally improves with exercise, as long as you're still getting 8 hours. Better friendships are completely orthogonal to exercise/weightlifting.
My parents are 67 and 65 years old; I would say say that daily brisk walking is possibly much more suitable for them (their body) in comparison to weightlifting -- irrespective of your personal definition of "exercise". And I'm damn sure their heart rate easily exceeds 100+ if that's the main variable to control.