At what age do chicks need grit?

I don't give mine grit, but then, they only eat starter crumbles - no treats until they are older.
As soon as I start giving them anything else (grass, lettuce, seeds, cooked scraps or oatmeal) then I give them grit too.

 

So long as you keep them on finely milled feed such as chick starter you don't ever have to feed grit.

It's when you begin feeding them whole or coarsely cracked grains, green feed, or anything else that isn't finely milled or chopped that you'll want to feed them grit. For young chicks I feed a sprinkling of canary or parakeet grit at about a week old just before I begin giving them finely chopped green feed. Over time I cut the greens coarser and coarser until they can handle them whole on their own.

.....Alan.