We started 'insisting' at around 2 years old, she never has to eat it all, and she never has to finish her plate, but she ALWAYS has to try everything on her plate. Including the things I know she doesn't necessarily like because tastes change so we always say "try it again and see if you like it this time" and if she doesn't that's fine but on a few occasions she has liked something she used to hate. Like tomatoes, and spaghetti bolognaise. I think this is good because she always knows we never force her to keep eating something she doesn't like, and there's no "I told you so" if she does like something.