My son is the youngest in his class being born in Dec 07 and there is a big difference btw those born early in the calendar year and those born in the later part of the year. The younger ones are more active and easily distracted while the older ones can sit still longer and pay attention. Was it too early to put him into K1? Well in my case, it was good experience for my son as he could not talk much when he start K1 and now he is talking all the time!. He learns from the older kids in class and he learns how to be independent and do things for himself. So for us it was a good experience to put him in early as the 1st year of Kindy in most international kindergarten is really just learn by playing.
So choosing the right kindergarten for your child is also very important.