The baby boomers are turning 50 - one by one, at the alarming rate of every seven seconds for the next 16 years. And just how many will be happily looking forward to blowing out a galaxy of candles and admitting to the world that they're half a century old? Very few, in Allia Zobel's opinion. But that's because they're not looking on the bright side. In a new collaboration after The Joy of Being Single (138,000 copies in print), Ms. Zobel and New...