you're not getting old
At least you should not use this very convenient excuse too often. Yeah, it is first to cross your mind, it shifts the blame to the universe, and it tells you the resistance is futile. Yeah, it might be difficult to see the connection between something you stopped doing a year ago and your spine crackling today. But this connection is very much possible. And my case was even more interesting: I have learned that the sleepiness and the degrading vision were the symptoms of diabetes, and disappeared completely one month after I started treating it. Naturally "just" getting old is better than treating diabetes, but being brisk and healthy is much better anyways. And lazyness won't help you neither to find the root cause nor to stay fit. Not to say it's difficult, but you'll have to put at least some effort into it.