Orion,
The people on this board are very knowledgeable. I agree with everyone here that you should wait and train naturally. Now, I'm not a big fan of most personal trainers, but, I am one. I don't encourage my clients to take roids, in fact, I try to steer them away to show them that there's natural development still left in them. About 95% of my clients grow much bigger because there's something that they're not doing. Stick with the basics and build a nice foundation.
Here are some suggestions: First, EAT!! Eat all the time. Try to get in a protein-rich meal at least every 2hrs. But, when you're not full, eat some more. I've gained close to 40 lbs. naturally in just a few months( okay, I put a little fat on this period). Suffice it to say, everyone thought that I was "on". Remember, food is the most anabolic drug that you can take. By eating all the time, you'll being doing what the drugs already do--creating an anabolic environment in your body.
Next, train using a varied approach. Never do the same workout over and over for months on end. Change brings about progress--you know, the adaptation principle. I like to go very heavy and do the basic three while "off": Squat, Deadlifts and Bench Presses. I gain alot of muscle when I'm clean as a result.
Try this program and post your results soon!
P.S. I was just like you at your age. I decided to max out my gen. potential first and did my 1st cycle @ 26. I'm very glad that I waited and you'll be too when your buddies are asking you what you're on!