It's a little early but you can start at anytime. They might pick at it to see what it is, but they won't eat too much right now. Chickens are really good at self regulating, eating it when they need it. I suggest offering oyster shell instead of eggshells. The eggshells only have so much calcium in them and if they consume them and lay an egg, that shell will have less calcium. Does that make sense? I save my eggshells, smash them, then use them in the gardenIf mine are 11/13 weeks when do I need to start offering oyster shell / eggshells? They are still on starter / grower.