[MandieD]

Modern example: my father, who is still living, driving, and traveling internationally.

When he was 15, his parents decided it was time for him to start driving his mother around, who never learned how to drive. They wrote down his birth year to make him appear 16. The Texas Department of Public Safety in the 60s wasn’t quite as strict about proof of identity as it is now.

Fast forward to the late 90s, and digitized driver’s licenses. Fortunately, my mother had an inkling that life for my dad might get a bit complicated with a driver's license that didn’t match his birth certificate, so she pushed him to get it corrected.

I imagine there are at least several thousand US citizens who have never lived elsewhere whose primary ID (driver’s license) shows a different birth year from the one on their birth certificates for similar reasons, and it’s a toss-up on which date they use for various purposes.