camarofrom69,
I hope you are getting some idea about what's involved in classic car ownership. After re-reading the post.... I believe that Belgium would have a totally different insurance system than we do here in the states. Even my friend in Canada has a national system, not private carrier type. I'm not saying it's better or worse, just different.
Since you have a few years to work with, here's what you might want to ask yourself before you head down that path:
-can you afford a fixer to work on, or a driver, or a completed car?
-can you afford the price of the car AND the import expense?
-Will your insurance be reasonable at 18 or "through the roof?"
-Is anyone in your friends/family circle able to help you with it?
-Do you want it so bad you can taste it?

(I know @ 18 I did!)
These seem to be the important things to think about for a guy in your position! Look into the insurance locally and ask an agent if they can run some numbers for you. Ask someone to look into importing costs from here to there. Also, don't forget to look on the internet for one in Belgium. I bet it might be cheaper to find the car there and have parts shipped over than shipping a whole car!
I'm not wanting to discourage you, I would like to see more young guys getting into the hobby. Just want to make sure you understand that owning one isn't all fun n games... Believe me, I learned fluent French by working on one 12 years ago

Dano:beers: