It is possible, but doing it for an app is not going to be easy, as you need to know the domain or IP that you want to block. Some routers have a built in feature that will allow you to block sites, or you can use something like OpenDNS.
http://www.opendns.com/home-internet-security/parental-controls/
I'm not advising that you do it, but it is possible. Also if he's web savvy (or if he asks in the toms forums i'll be forced to answer
) he could get around it, using a VPN or similar method.
It is also possible (depending on the router) to limit the bandwidth of specific devices, or to prioritise some devices over other devices, often called QOS in the router settings.