The median age of all employed workers in 2011 was 42.1 years. But some workers are much younger than others. Here is the median age of workers in the five occupations with the youngest median age...
21.4 years: Hosts and hostesses, restaurant
21.4 years: Counter attendants, cafeteria and food concession
21.8 years: Lifeguards
23.1 years: Motion picture projectionists
25.2 years: Ushers, lobby attendants, ticket takers
Source: Bureau of Labor Statistics, unpublished table from the 2011 Current Population Survey