In the US, marijuana has only been made legal at the state level (in some states). It remains illegal at the Federal level.
Those states have repealed the state laws that made marijuana illegal and directed their police forces not to enforce the Federal laws. But there is nothing stopping the FBI arresting people on marijuana-related charges in those states.
As the FAA is the Federal Aviation Administration I can only imagine that they still consider marijuana to be an illegal drug no matter where a pilot consumes it.
As for increased teenage use, I believe the facts show that legalising a substance for 18+ use reduces the amount of underage use. Unregistered (illegal) suppliers are pushed out of business by the legal ones, and the legal ones don't want to sell it to underage customers for fear of losing their license.