Can a 12-year-old play in the Minor division?

Yes, but only with a waiver. A 12-year-old wishing to play in the Minor division completes the Reg V(a) form, which requires sign-off from a parent, the local league president and the State District Administrator.

More generally, players cannot play in the Little League-Major or Minor divisions unless they are age eligible by League Age. If a player outside the age range is considered worthy of dispensation, an application supported by the State District Administrator can be submitted, and only Williamsport (Little League International) can approve it. For the Teenage divisions (Intermediate, Junior and Senior League) run as separate age divisions, no dispensations to play outside the age ranges can be applied for.

Source: Baseball Australia, Little League in Australia: Australian Governance (August 2024 edition).