There are a few good sites to play Poker free online, however, you do have to be 18 to register on them (don't worry, they are free and you play with play money!)
These two sites are the two biggest online free Poker playing sites.
Hope this helps 😛
If you are looking to play texas holdem for free then you should be playing at http://www.pureplay.com . The site is only for free, and the best free poker site on the web.
Other online poker rooms (full tilt, poker stars, pokerroom etc) do have a free option but they don't focus on the free part. They mainly have a free version of their for money rooms which is not ideal to play with.
My boyfriend always plays on aol games. Give it a try, just make sure to sign up prior to the start of the tournaments.