anywhere from 15 to 20 depending on their priorities and relationship status
Before you're born.
Not until they learn how to spell "lose".
When they feel right about it. <br />
No set age. Depends on the person and where they are
I don't think there's a general age really. Though it seems to me by some stories and such it's mid to late teens or later.
17 for the average American, girls a few months younger than boys.