@prestonmcghee I heavily agree with your overall sentiment but I will say there's at least a kernel of truth to what they are saying. I'm 40 and have been consistently working out the past 12 years. There's definitely been a bit of a decline in certain areas, mostly staying up late and drinking too much hits me a lot harder now, in my 20's I'd shake off a 3 AM night of drinking heavy by breakfast, now the next 2 days are shot. Keeping weight off is a bit harder and I'm sore a bit longer when I push myself. Also sitting still for long car/plane rides leaves my legs stiffer now.
That said compared to my peers (mostly 35-40 year old dads) it's night and day in what I can do vs. what they can do, I don't gas out playing with the kids, I can still do handstands and cartwheels with them etc... while they stay on the sidelines.
Basically the decline is coming, it might seem like it's not especially if you are new to consistently working out but you will start seeing cracks in the damn eventually. WAY slower than our inactive counterparts mind you, I'm definitely not falling apart at 40 like my mom made it sound like I would, still can probably run circles around my 30 year old self but I'd be more sore the next day, especially if I partied with him.