What’s the oldest kindle that can still be usable in 2025?

Basically as the title says I’m trying to get a cheap, usable kindle for my daughter to get her started. I’m not looking for fancy, I’ve got a paperwhite 10th gen and love it. I see a lot of second hand older models and wondered if they’d still be usable. TIA

EDIT: Thanks got my answer that she'll be ok with older devices. Thanks so much