The age is not the question. The question is the money/utility. Are you tastes stable? Doubtful. Is it worth the extra expense at this point in your life? Unlikely.
If you want up your looks, take it up in small steps. Try this.
1) No more T-shirts. Switch to V-neck. The angled v-neck line frames your face and add length to your upper body. Don't get excessively deep or very short. V-neck will run you a pack of 3 for 13 dollars, or at max (pima/egyptian butter soft cotton) for 20 dollars for 1.
2) Step 1 alone should yield great dividends. Next try a bunch of dress-shirts. I recommend cotton-poly wrinkle-free blends to start with. Its a lot easier for a younger kid. Hell, I still have a few of these that I absolutely love. The saying is "buy for quality to last you a lifetime", but I think in youth this is a terrible paradigm. You are going to buy and try lots of different fabrics, cut, and colors. This is inevitable to improve your fashion IQ. I recommend not spending more than 40-50 dollars/shirt. I had Van Huesen and Perry Ellis (around 30-35 dollars/dress shirt) for a while when going through school. Looks decent, fabric is mediocre, but it did the job for 2-3 years.
Consider this a down-payment and learning period to learn what cuts and colors work best for you.
3) Buy 1-2 jackets and 1 suit. Sounds like you have the suit covered. The jackets I would buy is a navy blue blazer and a dark-military jacket w/ those shoulder straps (exact name escapes me). These dark jacket work very well w/dark jeans, gray pants, tan/khaki pants. The military jacket will frame your figure and add width because of the pockets/shoulder straps.
Another nice jacket to have is a grey blazer or jacket.
3) Invest in some slacks. Don't go for high-end wool pants or what not. Just some different colored slacks. Calvin Klein has some, Perry Ellis/Van Huesen, or if you are really hurting Marshalls. The work-horse pants will be jeans, soild gray slacks/corduroys, solid light tan slacks (no corduroys, tan corduroys look too farmer-ish to me).
4) Shoes- 3-4 pair of shoes youll need. Oxblood, black, suede/tan, and flash. Considering your age, fashionable sneakers will do. Creative Recreations are a good bet- you can also buy them on amazon for heavy discounts.
Here are some thoughts...
When you get more comfortable w/all of this, you can start playing w/the individual aspects, red-shoe laces on black shoes (red v-neck, blue jeans, black shoes w/red laces). Blue shoe laces on black shoes (white v-neck, blue jeans, navy blazer). Bring some swag into your appearance.
In recapitulation, this should give you a steady wardrobe for your age and the girls you will encounter. Just mix and match, and youll likely be set. When cash flow improves, then you can start worrying about suits and the such.