The bill would go into effect sooner, but the Federal Minister for Home Affairs says the government needs time to finish all of the paperwork on the new regulation, and to allow each state and territory to draft its own laws enforcing the rating. The bill wouldn't mandate a nationwide rating, but simply allow each territory to create its own.
But that shouldn't be an issue, according to those in the know. Apparently, there's plenty of public support already. There were almost 60,000 submissions from the public responding to a discussion paper from 2010, and 98% of those were strongly in support of games rated R18+. As soon as the laws go into effect, retailers will be free to sell games as needed to anyone old enough to buy them.