HONG KONG -- China’s biggest gaming company, Tencent Holdings, said Tuesday it will limit gaming time for minors and ban children under age 12 from making in-game purchases after a state media article called games “spiritual opium."Tencent’s pledge to curb gaming for minors came hours after the company’s stock plunged as much as 11% following a critique published by the Economic Information Daily, a newspaper affiliated with China’s official Xinhua News Agency.The newspaper article named