I was searching for a thread where I had asked this question but couldn't find it. I know whole oats are okay for adults and rolled oats for young but I don't recall the age that you should give it. Per Storey's Guide, oats shouldn't be more than 5-25% of their diet (that is quite a range though)
I started adding rolled oats about 1.5 weeks ago to cut the protein. All of my birds will eat them though the chickens will pick them out unless that is all that is left.
Celtic knows alot about this and it may be on her website too.