If the child is ready for boarding school, and is eager to go, then the child should go. One of my friends, who was eager to go to boarding school, went at an early age, and has only benefited. He says the academics were amazing, and planned to go to Exeter- and made it in. If he didn't go until he was older, he might not have made it to Exeter, which prepared him to become a neurosurgeon. He was ready for boarding school, actually, he was the one who wanted to go to boarding school. I know that without going to boarding school, he wouldn't have been where he is today.
Under age 14 or so it never seems to be wise to send a child away from its family unless that family is abusive. Over that age, it would depend upon the wishes of the child and his or her goals and how close to the family he or she is.
While parents who are wealthy and busy may send kids off to boarding school, and others may do so for disciplinary means, in general, children should live at home and go to a school locally (whether it be private, public, charter, or home-schooling). Family life is important for children, and they will miss out on a lot if they are away from their family unit for extended periods of time. There is very little reason to send a child off to school when there are typically many options available locally.