Most teenagers I know, and myself when I was one, are much messier than at any other stage in their life. The issue for most is that they are old enough to start sneaking food into their rooms that a kid wouldn't, or that the kid can't hide as effectively. I've had to come spray for pests in more teenagers rooms than any other part of the age spectrum.

Fruit flies are attracted to the different human life stages by temperature inversely proportional to the humans age. They like hot babies, warm adolescents, cold adults and the rest can kind of be fit into that continuum.

Not sure either. Maybe because when it’s warm out, kids and teenagers are constantly running in and out of the house, maybe not closing doors behind them, which lets flies in?