Yep. Your body is “use it or lose it”. Im in the gym 3 days a week and I feel better and more capable than I ever did as a teen.
It’s also kind of a cycle. People who arent active feel their body suffer through day to day movements and think that the gym would genuinely ruin them. They dont realize that it would actually improve their problems, not worsen them, because the lack of activity IS the problem.
This is something only sedentary people say, like its some kind of universal truth but really all it is is the consequences of not exercising.