What is the right age to start Badminton?

I started taking my son along with me when I play Badminton and he developed an immediate interest. He will complete 4 years this September and that got me thinking what the right age to start playing Badminton is.

There is a coaching class for kids right before our slot and I checked with the coach if he would admit my son. He mentioned the minimum age for enrollment was 6 years!

I am sure I remember reading somewhere that Maria Sharapova started playing Tennis at the age of 4 years! I am also sure some of the other greats in their games started really early.

So then, what age is right to start Badminton or any other sport for that matter? Is there a difference between how we Indians approach sports and the other nations do?