err.. hmm im sure you can use bumpers at any age. but im not sure about AMF and places like that, maybe they have policies. but i know where i work it dosent matter what age. you can request them if you'd like.
I just posted the biggest post in the history of BOS in your gym thread.
Also, the machines often don't calculate calories correctly they don't take into account muscle mass etc. as long as you keep your heart rate up you're doing what you need to do (Y)