I showed both my children Schindler's List around the age of 15 or so (here in the UK, it has a 15 certificate). But they already knew about the Holocaust from a very early age, from literature and other films, TV dramas, and documentaries. Certain history should be taught to everyone from a young age, and the Holocaust is pretty much top of that list as far as I'm concerned.

My thoughts on Schindler's List (if you're interested):

Schindler’s List: One Person Can Make A Difference | Fanfare