The 17-year-old Brooklyn rapper Joey Bada$$ doesn't sound like his contemporaries. The handful of young rappers with tread, most notably Chicago's Chief Keef or the recently returned-from-exile prince of Odd Future, Earl Sweatshirt, make music with pomp and bombast, as aggressive as it is catchy. But the kind of music Joey BadA$$ makes hasn't sounded contemporary since the mid-1990s, or around the time he was born. Today, Joey is the most visible member of a young artist collective called the Progressive Era (Pro Era for short), a crew mostly comprised of students from Brooklyn's Edward R. Murrow High School. These kids take musical inspiration from a time before any of them existed, specifically, the era referred to by hip-hop purists of a certain age as the "Golden Age." That time period, however, was dead if not fully decomposed by 1999, the year of this tape's title. While albums from 1999 like Mos Def's Black on Both Sides and MF Doom's O...