I didnt try feeding it to mine until they were a month old. However I have read that you can start earlier than that. Not sure how early though. I have mixed uncooked in with yogurt. I also feed cooked. They seem to enjoy both. This morning was their first AM in their coop so I took out a warm bowl of it for them! It was a feeding frenzy!
I never feed oatmeal at all till mine are older, maybe two or three months old. The reason is that they need the protein levels to develop properly and oatmeal will effectively lower that. Now, if you finely chop some hardboiled egg and sprinkle it in thin, soupy oatmeal, maybe add a TBSP or two of plain yogurt in there, they are getting more protein and a digestive aid to boot. I'd not give them treats till they have some age on them.
Mine are about 2 months old and they wouldn't eat the raw oatmeal. I'm trying a little cooked oatmeal this weekend.
And they are aggressive little buggers when it comes feeding time. They peck at anything that gets near them. They tried pecking the diamonds out of my ring yesterday and as I was bent over in the coop the little buggers jumped on my back trying to escape. I will be SOOO glad when we get the fence put up!