Late 2012, maybe early 2013 I hurt my back lifting a 4 man carry box by myself (the army limit for 4 man carry is pretty low and it had handles, I'm not trying to flex here). NBD, hurt back, don't care. Kept living my life but taking it easy when I could. I did not feel old.
Fast forward to the following winter, sometime in December. I was 27. I've never been great, or even good, at athletics and I always struggled with my PT tests in the Army. I was getting ready to go running through our neighborhood. It had recently snowed (freaking Germany and the stupid snow) so I was getting all the gear on. Last thing is my shoes. I decided to put them on before I went downstairs. I bent over to put my first shoe on, no problem. Second shoe, I feel my lower back pop in the same place I had hurt it before. It hurt quite a bit but I skipped the shoe on the rest of the way. Took me 5 minutes to stand up straight. Probably 2 minutes to get down a single flight of stairs. I couldn't sit down so I walked around my house slowly untili felt a little loose again. Then I went and ran on the ice. I couldn't go fast because (I was fast and slow) my back and the ice but I sure as hell want going to fail that PT test.
As soon as my back popped while putting on my shoes, I knew that was the beginning of the end. I have to be careful every day now. Didn't help that 2 years later somebody wrenched my leg up while doing combatives and completely wrecked my lower back. I didn't quite feel old, but I knew that was the start of me acting old.