Answer:
It really isn't that much for adults. in fact many kids have M rated games alltogether. There is no limit to what kids can and cannot play anymore.
Games that are rated for adults are no different than anything else. If a 12 year old beats an adult at chess, it is consider impressive. While he is 15 or 16 it is not as unusual. It is not just the exposure to the blood and gore, intense violence, and strong language that should be considered. It is also the experience of the older players they will be against in online play. In spite of this it is correct than ratings of T and M are actually played by under kids who create accounts for an older age than they are.