Let put your age aside for a moment man. Your 5'9" and 155#'s man. You need to put on a foundation of muscle before you consider a steroid cycle bro. You need to learn how to eat and train to be big before you will ever get big. Master those 2 things and work at it. Get yourself a good solid, naturally attained foundation and set yourself up right man. Don't become one of those idiots that does a cycle, gets big, and then loses all his gains after he stops and looks worse than before he even started man.
Go to the training and nutrition forums here. Look at the 3j free diet advice thread. Post in there, that man can tell you in one post some diet advice you can adapt and use for the rest of your life to grow man, he knows his shit.
I say start there brother, if you do down the road you will be glad you did man!