Check out the basic articles on the "style" section of this website, particuarly the "redefining your style" articles.
To start adopting a more refined style, I think you need to learn the basics about:
- fit: big one, and a lot of debate about this. Learn what a good looking pair of jeans look like etc. then move onto understanding the basics of traditional tailoring.
- colour: not that complicated. If in doubt, don't mix navy and black or black and brown. (but as you get better at this fashion malarkey you can break these rules). Learn what colours flatter other colours.
- minimalism: cut out brands from your wardrobe, or at least garish large ones. Build a capsule wardrobe in which every single piece of clothing works with every other one.
p.s. For the record, you're never too young or cool to dress smart. I'm 18 and spend most of my life in a blazer of some sort. That said I am an odd case.