I agree. I think the cut off at 18 years old changes the statistic drastically. Those early experiences drastically colour people's future interactions and decisions on whether to do it or not.

That said I think kids are generally retards and cringe at the shit they did looking back on themselves. Mistakes are made and it's part of the learning process of becoming who we are. I'd like to find a study that focuses on this age group but unfortunately I can't, that may be because I'm not quite sure what kind of wording to use for it in a google scholar search though. Child infidelity isn't doing it.

Google scholar is great but sometimes it can be a right pain if you don't know exactly what kind of terminology the sciencey people would use to describe the study.