My parents tried to forbid me to buy Lego when I was around 14 or 15. I actually hade a small stock of money (they would notice if I would make a large withdrawal, so I kept on resupllying it by adding 30% of a withdrawal too it.
They would check my bank account, but they never noticed. After two or three years they accepted that it was a hobby for me. They believed me when I said it was a collection and no longer a toy. Which isn't really true anymore, I've gotten into MOCing since...
Nowadays, they're very supportive in it, they don't buy me sets anymore, but my dad does drive me to the Lego stores in Cologne and Oberhausen, which is a 1-hour drive. I remember when I bought the Sandcrawler, my mom said that my dad told her that he "thought it was a waste of money, but rather saw me spending it on Lego then on drugs" (Don't go thinking I do drugs, never did, never will)
So, the moral of the story: wait a couple of years, slowly try to convince your parents, and they might agree eventually. I'm sure they will :) And too bad you're leaving *wacko*