depends. If you are living with your parents right now then moving to an apartment will be harder than you think. You will have to pay your electricity bill, you will have to pay other bills, you will have to buy food. You will have to do all the cleaning, you will have to take care of yourself 100%.
So spending the money on the computer might be easier.
But seriously, your own apartment is a great thing. I moved to my apartment a few months after I turned 16, and I've never even thought about moving back to live with my parents.
ohh, and might aswell built a custom computer for 1/5 of that price.