Which sentence Is the Best?

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Mar 2, 2012 18:02
I don’t know which sentence sounds most natural of three sentences below.
How old are we permitted to have a driver’s license in Japan?
How old should we reach, when we have a driver’s license in Japan?
How old are we, when we are permitted to have a driver’s license in Japan?
If there is (was?) a more natural sentence than them, I’d appreciate it if you could tell me.