While I generally agree that a 19 yr old shouldn't use steroids, it's not for the reasons posted above.
#1 - steroids do not directly stunt growth. Estrogen stunts growth. If you use a steroid that does not convert to estrogen, or use an AI, then this isn't really an issue.
#2 - Not reaching max potential. Where is it written that if you take steroids before you are "x" years old, it will lower your maximum potential for muscle growth? At that age, you are pretty much at the top of your natural test era. It's only going to go down hill from there. I don't have a study to back this up, but I believe that the chance of permanently lowering your natural test levels would not be any worse at that age as opposed to starting when you're 25. If you look at it logically, the older you are, the harder it is to recover.
As far as reaching your maximum potential naturally goes, I'm willing to bet that there are VERY FEW steroid users who have taken that road. If you did, then that's great. It speaks volumes for your personal dedication. However, I don't see anything wrong with using steroids as a boost to get to your maximum potential faster. It doesn't matter how you achieved the muscle, if your body is genetically predetermined to carry it, then it will. There are obviously other factors that come into play such as allowing your body time to adjust to the new weight, among others. That doesn't mean that your body can't handle it though. It just tries to get back to what it has known as normal for so long.
My main reason for not suggesting that younger guys don't use steroids is simply because of a lack of knowledge. They don't have enough knowledge about AAS, diet, workouts, nor in most situations do that have the drive and determination to do things correctly and safely. These are all things that don't happen over night. It takes YEARS of dedication to find out what works and doesn't work for you.