Or is it more of an age-gated thing

Depends how old you consider old, maybe? Computers back in the day were pretty universally light text on a dark background. VIC-20 was an exception but then even Commodore backpedaled on that with the 64. But you might have had a different experience and are only remembering things like Mac OS or Amiga, or Windows, and maybe that has influenced your preference. 🤷‍♀️ To each their own, anyway.