First, what is the legal driving age in Japan?

Don't know. Sorry.

Second, of all the Ranma Charecters who attend Furinkin, who has the purest heart/soul?  Ukyou, Kunou, Ranma, Akane or Nabiki?  *starts giggling*
Reply when you can, but the sooner, the better!

I suppose that depends on your definition of purity. As for my opinion, I think Ranma would be the most likely candidate.

Of the whole cast, he is always the first to put it on the line for someone who needs help.

Akane is a distant second... but she's has the right ideas.

The rest... I'd giggle too.

 ___________
/ Here lies:\  Save the whales...
|   Andrew    |    Harpoon a Honda.
|             |
|   I think   |
| he's hungry | Honk Louder! I don't have a firing solution yet!
|             |