Of course, the answer is: It depends. I know that might not be helpful, but bear with me. The easy answer is that a child can start taekwondo or karate at any time from 3 years on up.
However, the success rate of that child is going to depend on a couple of things. Why is the child interested in martial arts? Why are you, the parent, interested in martial arts for your child? Depending on your goals, starting a child at a certain age may be more appropriate. Furthermore, the type and structure of a children’s martial arts program matters. Many schools are still grouping kids together in a large range of ages. For example, in the old days, before kids tae kwon do became so popular children’s martial arts programs were just all kids that weren’t adults. Over time, we started splitting the ages more and more, generally under 7 years old and 7 to 12 years old while 13 and up are considered teens.
At the Dragon Gym we’ve taken this a step further as it is necessary for a child to get the most out of their martial arts education (no matter what the style). We’ve divided our children’s martial arts program into 4 age groups. We call them “Early” for 3 and 4 years olds, “Basic” for 5 and 6 year olds, “Core” for 7, 8, and 9 year olds, and “Extreme” for 10 to 13 year olds. These age groups were specifically designed to address the physical, intellectual, emotional and social level of development for the student in order to maximize the benefit they can get from martial arts training.
So, with a program like this a child really can start martial arts training at any age between 3 and 13! Classes won’t be too challenging or too easy, but just right. However, without an age-specific program, I would recommend starting your child at age 7. With a large mix of ages, starting any younger will lead to frustration and burnout, starting older will lead to boredom and drop out.