Pinkbike is definitely similar if you want the same age and maturity level. Ridemonkey.com is another good site that's slightly better and seems to have a lot more information. Go to mtbr.com if you want relevant information (mostly) from people who are a little more mature. I usually just go to mtbr because of the number of people posting, the number of forums, and the huge amount of information availble. The only drawback is that their search function is totally useless.