I went to join VIA Préférence (thanks for the hint, zephyr17!) and birthday is a required field. Would someone who knows please tell me why?
Even though the sign-up web page asks for a birthday, it also asks for the member's age group. This makes me think that the programmers are lazy but also that it is some effort to appear to be weeding out underage people. If I recall correctly, AU requires a stated date of birth for such a reason.
Any insight would be appreciated. In particular, if I give VIA a false date of birth, will someone checking my passport accuse me of being someone else with the same name? And would it matter? (I would qualify for the senior fare based on both my passport date of birth and whatever I would give VIA.)