Immigration won’t refuse entry to an Australian passport holder because of that. Plus you just use the e-gates, so long as the photo is fine then I wouldn’t foresee any issues
Why risk it? Online info seems to suggest 6 months after your arrival is required. If the airline lets you board and you're denied entry into Thailand then they're on the hook to return you back to port of origin.
I wouldn't bother with the unknown and just get a new passport