CoolSculpting works by killing fat cells in grown adults. Once these fat cells are killed off - they are gone permanently in adults because after puberty, we are unable to produce additional fat cells. The fat cells that adults have expand and contract depending on caloric intake and expenditure.
In developing children/young teens, the results would not be permanent - they would be able to produce new fat cells because their body is still able to make fat cells.
CoolSculpting has not been tested on children/teens for this reason. I would suggest waiting for puberty to end and a safe number would be after the age of 18.