The game proper, as most things do, begins with a birth: your birth, deep within the loving steel confines of Vault 101. It's at this point that your masked father runs a DNA test on you, letting you choose your basic character details such as race and sex, after which your father will magically remove his mask to show that he shares the same genetic material.
He'll always have the voice of Liam Neeson though, that's a given.
Later, as the action skips to your first birthday, old Qui-Gon will presumably blow a party streamer in your face before presenting you with a book called 'You're special!' in which you can choose your attributes. Then when you're 16, having presumably warned you of the dangers of unprotected sex, Rob Roy rushes you into a G.O.A.T. test for you to choose some specific skills.