Since it's the firmly established doctrine of the Catholic faith that human life begins at conception, why shouldn't the Church begin officially reckoning the age of Catholics as being the number of years since birth, plus nine months?
I know, it would make us look weird. But we aren't called to conform ourselves to this world's customs. We're called to be conformed to Christ, and if, in certain times and places, that makes us look weird, so be it.