The problem with taking steroids too early are because your body is producing more hormones now than it ever will...you haven't reached your standard yet. Once everything levels off and is where it will maintain for a while, (around 25) you can manipulate it without worrying so much. Also, organs and bone are still growing, if you cause them to accelerate you could run into future health risks with that. As far as being diabetic, that could run you into some issues. Various AAS alter your insulin level if I'm not mistaken and that isn't something you want to screw around with. Because you are 20, you are going to do whatever you want anyway, so when you find something that is available to you, read all you can on it and make sure it won't mess with your insulin, that could suck for you. Also, some risks of messing with levels could include impotence and sterility...So, limp dick and shooting blanks. That is a risk you need to be aware of and willing to deal with. Its not a guaranteed thing, but it does happen to some. My personal recommendation would be to look for Warrior by Element Nutrition, its a legal supplement that has some pretty potent shit in it. I, and people I know, have used it with some wicked strength gains and lean muscle gains.