It's nonsense anyway. The policy is clearly directed at transpeople who wish to play in the league other than that of their biological sex. It is not directed at women who wish to play women's football.
All through amateur football there are age categories to ensure that players compete in teams equivalent to their development. And to ensure the safety of players. Such restrictions are nothing new.
Other sports, such as boxing, have weight categories for similar reasons.
Ms Mouncey ostensibly weighs 110kg. Serena Williams, surely one of the most powerful female athletes competing currently weighs, according to the internet, somewhere between 70 - 85kgs, some 25kgs less than an average man.
It would be very unlikely that a female AFL player would be anywhere near the height and weight of Ms Mouncey.