his age is the main reason for any of this, yes but deca on a first cycle is also a bad idea... just think of it like any other thing you are learning in life.., when you are riding a bike, you have to learn with training wheels etc... when you learn to shoot a basketball, you dont learn by shooting three pointers right of the bat... you start next to the hoop, work on your form and move out..
so with your body, which is FAR more of a delicate situation than the aforementioned instances, putting any sort of foreign substance in your body at first can be harmful and risky but jumping on something that is far harsher than others as your first is just senseless... there are so many things that can occur with deca and you are never letting your body even show you how you will react.. every steroid is derived from testosterone, so learning how you respond to just test is where to start, to learn how your body responds and tolerates this... generally, i like would start one off with something far lighter, like a peptide or sarm, THEN go to test ONLY, and then move forward after your learn your body response... i put health and understanding first.. some dont, and some just dont care about any of that, other than today and tomorrow with no worry of longer term.. .to each their own..