When Springsteen and friends visited the United Center Tuesday night in Chicago, age was an unavoidable sub-plot in a spectacular show. The crowd was a mix of mostly baby boomers, some with kids in tow, and Gen Y hipsters who may have discovered the band from parents, aunts, uncles, older siblings or the most recent Super Bowl and found a new hero in substitute drummer Jay Weinberg, the 19-year-old son of Max Weinberg.