Take a look around here, 90% of us are in high school and we build computers.
Think about it. I wanted to build a computer 2 years ago so I started saving up, with some help from parents (not alot) and some of my savings I got it and now what I have is an addiction to building them, lol. It takes me 1 1/2 hours to build a computer now, it will take longer on the first build, probally the best part of a day while you admire your components, but you will have fun doing it.
You will also have the support of everyone here if you get stuck.
Cisco CCNA, Comptia A+, 1/3 through CCNP