They said teens cannot waer contacts is it true?

No. Age is not as important as maturity in this case. Contact lenses, while very liberating, can be dangerous if not worn and cared for appropriately. You must be able to insert them and take them out daily, clean them regularly and follow all your doctor's directions - including keeping scheduled appointments. As long as you can do that, a child of any age can potentially wear them.
Depends. It really depends on the maturity level of the child. Improper lens care, poor hygiene, and overwear can lead to permanent vision loss. I would only allow under very close supervision and would not allow extended wear (sleeping in lenses).