SYDNEY, July 7 : Australia's online platforms are stumbling at the very first step in implementing age checks for users, rendering a world-first teen social media ban ineffective, a study by a team that advised the government's rollout of the curbs found.Since December, Australia's new social media law has mandated that platforms including Instagram, Snapchat and YouTube bar people under 16 years from having accounts. Operators must take "reasonable steps" to comply, and the government has recommended using multiple checks to determine users' age.The ban, however, has been widely criticised, with studies suggesting most people under 16 are still able to access the platforms, prompting Australia to double the maximum fine last month and warn of court action against tech giants for non-compl