My patents didn't restrict my reading, and I was reading adult fiction and biographies by age 13 (it's ages ago but I remember that I definitely was reading adult books by that age, since we moved to a new location with new library), might even have been a bit earlier. I remember reading at least FannyHill and books by Stephen King at that age. And I'm a university graduate with a good job that doesn't involve xrated services, and haven't mutilated anyone so far
But be sure to have a good contact with your kid, so that (s)he can talk if the need arises.