Target date funds, which start young investors off with a relatively risky portfolio and shift toward a more conservative profile as retirement approaches, have practically exploded in popularity in the last decade, growing from less than $100 million in industry AUM in 2004 to more than $600 million at the end of 2013 according to Ibbotson Associates. This strategy assumes young people will be able to keep adding to their TDF and ride out a rough business cycle, but unstable employment means that the theory doesn’t always work out. “Current savings options blissfully ignore the fact the young use their…