How old are the Merlin characters?

I've often wondered exactly how old the protagonists of our favourite show Merlin are. We all know that Merlin, Arthur, Morgana and Gwen are supposed to be young adults...but how young? The knights I'de say are all in their twenties except for Leon, I'm guessing he would be in his early thirties. Then there was Morgause and Nimueh...We know that Nimueh is much older than she appeared, and I'm not sure about Morgause. This may seem like kind of a dumb post but it makes sense. How old do YOU think everyone is???