Actually, I based my age guesses on evidence from the manga itself. I wasn't aware at the time I started writing, but apparently there are 'official' timelines for the series... according to which Kakashi is actually only a year or two older than Iruka. I have made an executive decision to ignore large portions of Kakashi's personal timeline, because they really make no sense. I will accept him graduating from the academy at six. I will not accept him passing the chuunin exam at age six.