Best beginner turtles that stay small and live 50+?

Hi I’m looking for a hardy small beginner friendly turtle that can live 50+ years in a 75 gallon.

I'm not a turtle guy. Perhaps you can research the Desert Box Turtle.

I have kept a group of T. c. triunguis (relevantly similar to T. ornata, AFAIK) for a few decades, and can pretty confidently say that these are not 'beginner friendly'. Keeping them indoors year round in a fish tank wouldn't be optimal in any event.

Mine are WC (from a time when CB weren't really available), so this might be part of the explanation of my experiences; the specimens that spent the most and worst time in the retail chain of custody are the ones that have fared least well. But they're that kind of animal that hides its issues until it is on death's door, and are hard to deal with for medical diagnostics and treatments.