Labor participant for teenagers 16 to 19 years old are down: from 51% in 2000 to 42% in 2007 before the recession. Youth are staying in school for more years.
At the same time labor participation at old age (65 and up) are up significantly. People are retiring later in life.
This is probably due to the economy has evolved toward automation and knowledge intensive work.
Service robot will replace more and more menial service that teenagers often do.
And if people are graduating with Ph Ds at their 30s, you would like to see them work into their late 60s or early 70s so that investment in human capital has a longer effective life.