^^ I agree.... its true, its active, its a designer steroid. The terms PH and DS get used interchangeably when they aren't the same thing and if people can't differentiate between the two then they shouldn't be ingesting them in the first place, IMO.
Under 21 is a very good guideline and if its clear you are still growing or hit certain stages late, even then might not be the optimal time. If you are 17, you should focus on training, diet and basics like creatine and protein. Your natural testosterone and GH levels will get you very, very far. Learning these basics when you are young will help you take better advantage of the other supplements and PH/DS, if you so wish, later in life