I am comfortable with compromise. You have to number something so starting it from an approximation of the birth of an amalgamation of possible historical and fictional characters that came together to form the fable of Jesus is as good as any.

A bit like Celsius starting zero at the melting point of water rather than absolute zero. It just works for us. If we dated from the known age of the planet we'd be altering it all the time as knowledge is taken from scientific discovery and Apple would have to come up with a new app to synchronise calendars...