Seriously, talk about starting big... Goku's hair is NOT for novice modellers. You should start with a character like Piccolo, Krillin, or Trunks.
But, if you simply must, then here's some advice, ad curves. Goku's face should not be straight lines, they should be curves. If you have a line with 3 or 4 points to it (like from his nose to his ear) be sure and curve it a bit down, and out, to give that round "cheek" look. Also, Goku's eyes are big, you have them quite small. They should take up about half of his face when wide open, and 1/4 when narrowed. You have them at about 1/6th the face's height. To make him look older, less chibi, remember to proportion his chin better. It needs to protrude out, and be a good bit longer.
The eyes should be about halfway down his head, the bottom of the nose should be halfway between the eyes and the bottom of the chin. The mouth should be halfway between the bottom of the nose and the bottom of the chin. That should help get your proportions.