For gaming you want at least i5 processor, and it must have a dedicated graphics card. 4GB RAM. Ultrabooks usually have no dvd rom so not very feasible. Ipads are more for show. If he's into BF3 etc, forget that.
I would be talking on behalf of your son.
The specs should totally depend on how much he will push the parts.
One example: Gaming is a very elaborate topic and there are also different levels, from Minecraft to Metro 2033. Light gaming means a mid-range processor and graphics card such as the i3-2120 and the Radeon HD 6450.
High-end gaming isn't usually done on a laptop so you could also do some research on desktops...