Don't tell them your age, that's just pure stupidity, if you're going to do it underage, atleast be sly about it. Telling them you're underage then signing up for an account is like going to an prison and saying you killed your mum.

I believe you mean personal, not private. Anyhow, it really depend's how much you need in and out of your paypal account, the personal has a certain sending and recieving limit if I'm not mistaken.