I doubt that many young people do "high protein / low carb" diet. It's hard to avoid carbs by mistake, especially with young people food like fries, pizza and beer.
"Low carb" diet does not lower your testosterone. "High protein" diet does [1], because proteins will bond with testosterone. Increased magnesium will prevent that [2].
"High fat / low carb" diet will increase your testosterone due to increased dietary fat consumption.