New Yorkers over the age of 21 can now possess and use marijuana — even in public — under a legalization bill signed Wednesday by Gov. Andrew Cuomo, though legal sales of recreational cannabis won’t start for an estimated 18 months. Passed after several years of stalled efforts, the measure makes New York the 16th state to legalize use of the drug. New York becomes the second-most populous state, after California, to legalize recreational marijuana. “By placing community reinvestment, social equity, and justice front and center, this law is the new gold standard for reform efforts nationwide,” Melissa Moore, New York state director of the Drug Policy Alliance, said. The legislation also prohibits police from using the odor of cannabis as a reason for searching someone’s car for contraband. New York will start automatically expunging some past marijuana-related convictions, and people won’t be arrested or prosecuted for possession of pot up to 3 ounces.