Don't give up the fight because it's getting tougher, man; you knew it would. And you see the alternative in your contemporaries: not pretty.
I hesitated to respond because although fit, "seasoned jock" doesn't exactly describe me (
), but yeah, at 48 I may be trailing some of you guys but I do know what you're talking about. 15 years ago I worked with a 50+ retired cop and bodybuilder. The dude was huge and I clearly remember him saying stuff like "I now have to work out twice as hard to get half the results" or "I'd eat a turd to be 35 again". I was in a kick-ass shape without trying and didn't quite get it back then, but his words have come back to me a few times in the past few years...
While until 40 I felt like time had no traction on me (people often thought I was 10-15 years younger), after that it's definitely gone downhill. Talking workouts specifically, I have a harder time getting motivated and I started getting joint and muscle pain recently, which never happened before. You don't have to go down without a fight, but you definitely have to warm up and pace yourself more. I haven't looked into testosterone, but all the serious guys do it and there's probably a reason. You do get softer with age.
Another often forgotten reason why staying in top shape gets harder is that many men our age have had, or are having, health problems. Most guys I know (myself included) are on some sort of medication, and drugs often have nasty side-effects. Plus, as the end becomes visible on the horizon it gets more difficult mentally to keep being so hard on oneself.
I'm starting to consider changing jobs because of my diminished physical capabilities, but truth be told, most guys even younger are woefully out of shape and worse off, so this reassures me some. I see 25 year-old kids with a good size gut who think they're in shape while I still have a flat stomach so it's not that bad if you watch yourself.