Myopia is actually genetic as well as due to environmental factors. a particular type of chromosome is thought to affect myopia in the genetic cause, but this is often combined with other environmental factors as well. http://endmyopia.org/so-is-myopia-genetic-after-all/ There is no minimum age for wearing glasses, and your child should start wearing them as soon as they are prescribed. on the other hand, doctors suggest it is best to wait till your child is at least 13 or 14 years old before wearing contact lenses, as the risk of infection could be high.
Myopia is thought to be caused by a combination of genetic and environmental factors. There is no minimum age for contacts and glasses. Every case is different so please refer to your child's pediatric ophthalmologist's recommendation if your kid does or does not need contacts/glasses. Source: http://www.aao.org/eye-health/ask-ophthalmologist-q/is-myopia-hereditary