Every child is different so I don't require that a child be a minimum age to join. That being said, I created this course based on teaching my 12 year old son. I think he could have handled it at age 10 because he is on the computer a lot, so my recommended age range is 10 and up. This is perfectly suitable for teens as a starting point in design and I will be adding Levels 2 and 3 later on which will dive into more advanced projects such as website creation.
If your child can read, use a mouse, and follow instructions, they should be able to do this course, but younger kids might need more help from you.