I must be getting old

I have discovered that I no longer have the stamina that I once had in high school. The coach of the second JV team and I decided to combine our practices. We work on drills and endurance training on Tuesday and on Wednesday we scrimmage. Since all of us coaches are so young we are very active in the practices, practicing along side the kids demonstrating what we want them to do. Today my shoulders ache, my legs are on fire and my ankles are weak. I feel like I'm now that "old guy". Now I have not lost my skillz, I can still play the game. I just Hope it doesn't get to the point where I have to use my hockey stick as a cane.