Starting young with AAS can stunt growth and mess with your internal organs, but overall if you are done growing (heigth) at 19, and you look conditioned and have been training, for 3 4 or 5 years, you should be the judge of when to start and when to continue or stop if you are having issues. Each hormone has specific sides, Test, est, nan, prog, all cause different conditions like water retention, agression, acne, liver and kidney and other organ (pancrease, stomach, intestines)function impairment or enhancement.
You need to start with 1 compound and not do too many at once to start or you will have extremely bad sides.
I suggest test only 300-400mg/week to supplement your natural hormones, and then go up to the higher dose once you shut down and cruise for as long as you can stand the sides, and are relatively heatlthy compared to when you started. Take some pct for a long time and don't stop lifting AT ALL. How hard you lift when you come off and how much you maintain your routine from being on will produce the best rate of retention for gains. I don't train for size, I train for strength, agility, speed, stamina and endurance, purposefully staying at 169-185lb, and I can say the harder you go on, the more you lose if you don't keep it up when you come off.