In the summer, my 16 year old son goes to the conditioning gym 5x per week for 60-90 minutes (and comes home soaked in sweat), has travel baseball practice 2x/week, and goes to strength and conditioning practice at the high school for fall football workouts 4 nights per week.
My 12 year old son has to be frog marched to the treadmill to get some form of exercise 3x/week and complains mightily the entire time.
I know that my 12 year old is the norm, and my 16 year old is the oddball in this regard.
When I was that age, I got my exercise by taking my dog for mile-long walks. But that was at a time when a Copper State solon who is beloved on this site was making a White House bid--and times are different, now.