Limiting downloads on a wireless router

I would like to give access to the Internet for clients in my waiting room.
But is there a way to stop carrying out huge downloads? They would be using
their own laptops or iphones.

Is there a wireless router out there which can set a download limit for a
particular MAC address? or perhaps a setting on a normal router (to which
the wireless router is attached) which limits downloads to a certain IP
address on the LAN.

thanks in advance.