What Age to Learn Wing Chun?

The other day, a lady friend asked me about kung fu schools that teach to children 4 years old and up. After consulting a few friends in the kung fu circles, they weren't able to find any that taught younger than 6.

it got me thinking - what age is appropriate to learn wing chun? I know some have kids classes - but is it motivated by money or for actual well-being of the students?

Can kids understand the concept of the centre-line, knee pressure, chi-sao, foward energy, etc?

Are their bodies capable of learning the "pigeon toe" stance? is it good for their body development?

Some schools only teach adults, while others may teach teenagers and older.

Wing Chun seems to be in its old category when it comes to teaching children - there aren't kids at the age of 6 swinging their arms and legs like that in karate or taekwondo. Perhaps the kids will be bored out of their minds just doing Siu Nim Tao? Even i've had my days....

Until then