littlegreencloud
Also, your earlier post included this No matter how fit and active you keep yourself, your muscles slowly decline and your ability to use your body as well and fast as you used to declines with it. The decline is accelerated in women post menopause.
You've clarified now what you meant but while yes, we will all age (and therefore muscles will deteriorate with age) the second part of your sentence isn't true as it stands. You can continue to use your body as well and as fast as you used to, depending on how you train.
I run a little faster at 45 than I did at 25 - that's partially due to me changing my exercise routine - I only ran (a lot) at 25; post-children, I combined running with HIIT, weights, core and walking, and overall, have improved my strength and stamina and running times correspondingly.
That's just me, and of course I could have also been unlucky and got an injury somewhere along the line that prevented this, but happily (touch wood!) not so far.
Personally, I now wouldn't choose to do some of the more extreme running I did in my 20s e.g. very fast races, mountain running and marathons, but plenty in my age group do. It just doesn't appeal to me any more, prefer a more rounded approach.
Sorry OP derailing the thread a bit!