20" muscular arm at 54 is impossible without gear.
You have 10'' arms at half his height and weight, so I'd say it's possible?
Hahaha, you're barking up the wrong tree, son. Go do som3 curls and get back to me. lol
Seriously though Coach, you look pretty damn good for 70.
And even at 70, 1/2 this board couldn't stand next to me, including you. lol