I feel https://travel.stackexchange.com/q/134011/4188 should have been asked here so I am doing it.
To travel with a discounted Youth Pass, you must be aged from 12 up to and including 27 on the start date of the Eurail Pass.
Is there a legal definition of what "age" is here? Some people in the linked Q&A insist it is based on birthdays but I can't find anything to back that up. In other words, if I was born on Feb 31, how old I am on Feb 30 legally? (nonexisting days are deliberate to avoid the discussion on me doxxing myself)