My wife was carded for it and told you had to be 40. I suspect there was a mis communication but I thought it was funny. I do know there was federal legislation to restrict it to 25 but I would not surprise if I state upped it to stricter.
I was actually looking it up and alls I can find is my state has completely outlawed pure forms of Dextromethorphan but I can't find anything on age limit except a federal thing for 25. Which is still funny given the gun thing.