Hm, I don't understand why you dislike the phrase. To me it means (roughly) "as you get older things you took for granted when you were young become harder work. You'll need to keep up regular training, you'll need more rest, you'll be more aware of aches and pains, and injuries will take longer to heal. So toughen up." In other words - don't stop doing active stuff, and don't complain if it's a bit harder work. I think that's a pretty good message.