As far as I know, and I'll humbly submit in the face [sic] of better knowledge, normal bone mass maturation is a natural growth hormone driven process.
You will gain bone mass and density most rapidly through your puberty, obviously due to your naturally elevated growth hormone levels. These will eventually drop back to normal in your late-twenties/mid-thirties. So, your bones, including those of the face and skull will continue to grow and alter until you're in your early/mid-thirties.
Even at 21, you're nowhere near that age yet. I can't emphasize enough the HUGE risks you undertake if you irresponsibly experiment with steroids. These chemicals are potent enough to kill you or, at best, cause your body grotesque and irreparable deformity and damage. I'm not going to lecture you on this issue, it's well documented both here and elsewhere on the net.
If you want to give your body the best chance to develop fully, I would advise you to concentrate on your dietary intake (protein etc), exercise and sleep. I guarantee that with these three in check, you are in a far better and safer position than trying to chemically alter your hormone levels.
Just as an aside, because you mentioned jaw bone issues, please check out this link about Invalid Link Removed.
There's a lot of good advice in this post from people who know what they're talking about. I hope you pay heed and stay safe and strong.