Your body hears everything your mind says.
If your mind thinks the body is old, then you’ll find that your body is old. You’ll find you can’t do things you should, that every part of your body hurts.
If you tell yourself that you are young and fit, your body reacts accordingly.
I would rather be a 40-year-old stuck in a 20-year-old body than a 30-year-old stuck in a 60-year-old body.
Get up, do the work, stop complaining because you’re getting better!