Hi Mr. Hooker, I'm in my late twenties and still finding hard training productive I would like to understand what you mean by this type of training. What would spring to my mind are high falls(although I have seen ukes who can high fall like they're landing on feather pillows.), and rough training with a martial intent...sparring? I'd say that there's probably a time when I should stop beating a makiwara with my bokken, I've heard the elbows can start to get sore.
I'm interested to hear what older practitioners have to say about this.