What age should you stop supervising your kid's brushing?

The number of tooth decay cases is soaring and dentists have advised that parents should supervise their ward's brushing until age eight. It is being reported that the primary cause of a trip to the hospital for children under 9 years is a rotten teeth.
In its recommendations to stop the rot, the RCS advised parents: 'Brush teeth with fluoride toothpaste for two minutes twice a day and supervise children's tooth-brushing until they are at least eight years old".
In another report, the Royal College of Surgeons believes children should be watched closely by parents when brushing their teeth until the age of 14.
What age do you think is best to stop supervising your kid's brushing?