Is there a minimum age requirement to sit in an exit row?

This morning there was some problem in E- and the GA came on the plane with a spray bottle and some towels. Later the FA moved up three people from E- to sit in the exit row. One of the three was a young boy, around 12 years old. It was obvious that he could not assist in the evacuation of the plane.

It bothered me, so I thought I would ask the experts here.