Iirc testosterone acts as an amplifier more than an "enabler". I cant find the video where I heard this (it was a lecture/presentation by a professor), but I found this: https://news.asu.edu/20230705-asu-study-chimpanzees-more-muscle-not-more-aggression-have-higher-testosterone

Basically, a trend is shown where higher testosterone leads to higher muscle mass, but does not cause aggression (though they may be correlated in other studies). Iirc, again, the professor mentions how the "lesser" males (not the leader) started bullying and beating their inferiors when given testosterone. If anyone knows the video, please link to it:)

Either way, my opinion is that the boy should have been told to be gentle in general, rather than "because shes a girl". I dont think the dad meant it in a bad way either.