I was on a recent flight in an exit row on a UA domestic flight. As a 1K, I boarded early with Group 1 as usual. However I noticed towards the end of boarding, there was a parent and a "young appearing" girl sitting in the exit row on the other side of the aisle. She looked maybe 11-12 years old, but who knows how old she really was. Not sure if they didn't get seat assignment until the last minute because regular E seats were full and only E+ was available or they could have been non-rev. Although the FA came by and reminded everyone that we were seated in an exit row, she didn't ask the girl how old she was. Isn't the minimum age 14 or 15 to sit in an exit row?