Hi, sorry for responding to a week old post,

This is called “Sarcopenia”, or, the age-related loss of muscle mass.

The good news is that it can be nearly entirely mitigated by strength training. To be clear, you can’t be an 80 year old with the same strength as a 30 year old powerlifter, but you can as an 80 year old maintain the strength of an average 30 year old. It’s been demonstrated very consistently, even if you only start training in your 70s