With government I have signed no contract and so am not legitimately bound to any set of rules. I submit because of fear of reprisal. This is a big difference.
By opting to not leave the nation upon, say reaching the age of 18, are you not agreeing to an implicit contract by virtue of your residence and use of its services?
Here's an example for you: let's say you were born in my household. Even better, let's say you are my child and were born in my household, and I demand payment from you to continue to live there. You counter by stating that you own your own bedroom because you bought it from me. That's fine, I say - you own the space inside the walls, but that doesn't really mean you can act with impunity and not pay me a fee to continue to live there.
You are free to leave.
Basically, you're over interpreting the concept of land ownership to mean that you can operate your own sovereign domain within another sovereign domain. Life does not really work like that - unless you're the Catholic Church and your host is Italy.