When I was 5 My parents took me to a farm to pick up our new dog.
While my parents and the farmer were engaged in conversation, I wandered off a little ways.
My parents and the farmer heard me saying "nice chicky chicky" and turned to see that I had gotten into a chicken pen...With the farmers prize fighting game cock, complete with metal spurs and all!
The rooster was used to humans being scared to mess with him, and didn't no what to think when a pint sized human grabbed him off his perch and carried him around petting him.
My parents through the years have told me how wide eyed that rooster was, and how they thought the farmer was going to have a heart attack right there!
The farmer took the rooster out of my arms, and the rooster proceeded to flog the devil out of him.
The rooster was too stunned to move while I had him.
I've done a bit of Googling in the last half hour and can't find anything, anywhere that says at what age they are capable of spraying. I'm guessing they are born with the scent-glands, just haven't found anything that backs it up.