Old or young, it doesnt make that much of a difference. I say this because physical burnout is not just about injuring the back muscles or the big limbs.
Its the little things that could get you in trouble or injury. Things from rotator cuffs, wrist ligaments, to finger tendons, those are the worst for dragonboaters and OC Paddlers (besides pulling your back/hip). Once you feel pain, you're fucked...and it could be a permanent injury.
As much as getting lots of rest after that intense schedule will help you, it wont do as much good as actual rest in between to give time for muscles/tendons/ligaments/etc to properly heal up. You work out, so you know to never work the same muscles in consecutive days...You do that in gym, your muscles just never develops properly and you could get injured. In DB/OC, injuries almost always happen, no two ways about it.
My 2 cents.
