New to dressing nice

Hello all.

My name is Kennen, I’m 15 years old and really want to start dressing nice. First let me start off by saying that this question (or series of questions) may be a little lengthy so sorry in advance.
1. Am I to young to start dressing nice? (May not be fully grown, don’t have a ton of money, etc.)
2. What are some items I need to buy? (Have a few casual shirts that I use as dress shirts and 5 or 6 ties to go along, mainly khakis and a few pair of jeans, I also have two pair of dress shoes, one brown one black. I don’t have a suit or any sportcoats/blazers. As far as accessories go, I have 2 nice watches, again one brown and one black, and two belts also brown and black.)
3. What brands are going to fit me best? (Like i stated before, I may not be fully grown so I need
a brand that has many sizes that can fluctuate with my growth.)

Thanks, Kennen.

Buy a new Sports Coat.

I am a young man at university with limited funds and I have started looking out for second hand suits, shoes and jackets. I have been able to get a couple of nice second hand woolen suits and some good Allen Edmonds shoes. I have been having more difficulty finding a sports coat. Should I fork out $300-$400 for a new one or should I keep looking for a second hand one?