Never buy a bike from Walmart or any other department store. They only come in one size and are junk. A full suspension bike like that is the worse thing that you could get to ride on the road. At his height the only place to find a bike that will fit is a bike shop or a used one on the local ebay or Craig's list. He will need at least a 23 inch frame and a commuter bike like this, not a mountain bike.
http://www.bikesdirect.com/products/gravity/grav_dutch.htm
http://www.bikesdirect.com/products/gravity/grav_dutch.htm