Getting big without steroids is different to getting big with steroids so the information that they gave, may or may not work for you. You should see some kind of results fairly quick at your age with a good diet and exercise program. That being said if you are looking to get as big as the professionals that ARE on steroids, without steroids then it isnt gonna happen as everyone has a genetic potential of a certain size NATURALLY. to get bigger than this you would have to turn to steroids.
Personally i think you are doing the right thing by staying natural. you are at a good age to start training and have everything on your side growthwise at the minute.
You should google some natural bodybuilding competions to see the kind of physique that is achievable NATURALLY, imo the physiques are much better proportioned and natural looking than the guys in Mr Olympia and competions like that.
There are several natural competitors on this site (Rich Knapp and Dmaipa amongst others) and they have very enviable physiques.
You need to be in this for the long haul, it wont happen overnight, but like I said at your age and with the right diet, program and level of commitment then you could build a fantastic body.
There are loads of articles on here about natural training, genetic potential and things like that. If you need any particular information then just start up a thread and ask, the members here are very knowledgable and will definitely get you where you want to go.