Character age: 12 years plus d12 (the exact animal year would depend on the year in which the game is set...the year would also determine one of the elemental affinities of the character)
Month of birth: roll a d12
Hour of birth: roll a d12
Day of birth is where things get tricky, because this runs vaguely off a 60 day system with five elements cross referenced to the twelve animal signs. A d60 is relatively easy to simulate, d6 for the tens column, d10 for the units.
I'm thinking that these rolls might offer a range of skill choices according to animal and elemental affinities, and if a character rolls a particular element or animal more than once they might gain the opportunity to follow this path to gain special advantages.
It could be interesting to have a mouse mutant whose horoscope gives them a strong 'tiger' nature.
Characters wouldn't have to follow their random destiny, but those who embrace their stars might find a spiritual enlightenment easier to achieve.
Just a thought at the moment.