I'm quite a bit older than you, joyful--and you're right that while weight-bearing exercises will slow the loss of muscle, nothing can completely stop it. I don't like to think of it as "prolonging dying," however.
Also, decay isn't the right word--decay happens to dead things once bacteria start eating them, and that certainly isn't me yet... A better word is degeneration, but that still seems so, well, degenerate.
Let's just say things change as we get older, and we must adapt and pay attention to our health. But it's all good.
Jay