Well, I can tell you it is at least two yrs old because he has developed the ring, short of that, noone can tell you how old a bird is by looking at it.
He could be 2, 12 or 20, literally... only a vet could tell you an approximate age. Even then, it would be an approximate guess.
Sorry I couldnt answer your question but welcome to the board. Im sure you will find alot of info helpful and make a few friends.
He is a pretty fella but I would have to say he is no 'spring chick'.
EDIT: You are very welcome.