I agree, and tend to see it more as a defense mechanism. The main thing young people tend to have more of is time.

There's also a use/abuse aspect. My older body creaks not necessarily because it's old, but because I have used (maybe abused - I started Jiu-Jitsu at 40) it physically for 40+ years. I suspect the mind is similar. If it's been abused through stress and/or drugs or let go out of shape by watching TV all day, then yes it's less sharp. But age isn't the driving factor in that case.