My son wrestled from 1995-2004, through his senior year in high school. All the kids wore singlets. In grade school some of the kids wore tights but that was rarely seen in high school. Knee pads were fairly common but jock straps weren't. All the girls I saw wrestle wore a t-shirt under their singlet. School sanctioned wrestling was referred to as folkstyle. Their singlet was different that what you see in the Olympics. It was more like boyshorts with a t-shirt, sewn together.
In the offseason, most kids wrestled freestyle and Greco-Roman, the styles you see in the Olympics. Freestyle was more common than Greco. Their singlets were basically jam shorts with shoulder straps. The girls still wore t-shirts.
What seemed so obvious to me didn't seem to be so obvious to other parents, any sport that has moves such as the "high crotch", probably should separate the genders after puberty hits.