Are these allowed on post?

http://www.walmart.com/catalog/product.do?product_id=12080254&findingMethod=rr 

Or any of the other razor products like the dirt bike? 

On the tracks made for 4 wheelers and dirt bikes out by Blora? yes!

In housing areas? yes sorta, depending on who comes by and feels like being naughty or nice :) When do we not deal with that with unclear rules though?

In Montague there is a field area that people would ride their 4 wheelers in and there was an accident one day. Not positive if they got in trouble or not, but the Razor products that are lower CC like the kids cars are fine in post housing areas as long as they are wearing helmets.
As for the dirt bike ones...YIKES! Then you get into the rules of needing the motorcycle safety course and wearing all PPD when riding.

How old of a rider are we talking about here? 

My son is 7 and I want to get him the electric Razor dirt bike (not the one pictured above)but I don't want to be told that he can't ride it on post. 

Electric should be perfectly fine. Gas is all I would worry about. My 2 boys have the razor scooters and never had a problem with any MP's other than not wearing their helmets. Another set of kids down the street had the dirt bike one that was electric and same thing, no problems unless they weren't wearing helmet and safety vest.

Go for it! 

Thanks Kelly. :) 

one of my old neighbors had the pocket mod, and she rode that thing everywhere , check with housing first!