This question focuses on nails, but could be expanded to the rest of personal hygiene. Like for nails, did they just grow absurdly long nails, or like break them via rocks? How did they shave anything pre-metal? And did they wipe their butt after taking a dump or just live with the itch?
Suggestion: post this to /anthropology. There are still hunter and gatherer peoples in the world today.
Heya, I have an earlier answer on Bronze Age/early Iron Age nail trimming, if you're interested.