you can try blocking torrents, or the word torrent, major torrent sites, but with magnet links, encrypted transfers, etc, it's hard. Tell you grown up son to stop, no internet, or pay for his own in his own name and he can deal with the DMCA letters and fines then, or kick them out of the house.
You can only likely make it tough on him because I can get around anything he could also.
Your router has some basic feature but you may need a better one if it does not meet your needs.
The first thing to try are the parental control option. The method that would work for sure is to block everything and then put in allowed sites one at a time. I am sure you don't have that kind of time. You could try only allow http and https and some of the more common things like dns and ping and such. This would stop most things but will break most games also. Unfortunately bit torrent can be made to run over http ports.
You could also try opendns which this router supports. Then you use the parental controls to block access to DNS servers. BUT this will only stop him from getting to bit torrent sites. Bit torrent uses IP addresses without dns. It also does not take too much research to learn how the HOST file can make opendns ineffective.
If the kid is in anyway determined to download stuff, quite simply there is no measure that will stop him short of just removing his Internet entirely. No doubt your modem will have some feature to block certain sites, so hit the obvious ones like Pirate Bay, Isohunt and bunch of the more popular proxy services. Though this is a temporary measure, anyone determined will find ways around it easily.