Source: Jonathan E. Booth, John W. Budd, and Kristen M. Munday, Industrial & Labor Relations Review, Vol. 64, No. 1, October 2010
From the abstract:
The authors analyze youth-adult unionization differences by using the National Longitudinal Survey of Youth 1979 (NLSY79) to follow a single cohort of individuals from the ages of 15/16 to 40/41. They find that the differences between youth and adults are greatest at ages 15 to 17 and largely disappear by the age of 23. Though currently unionized workers are most likely to be in their forties or fifties, research also demonstrates that younger workers have a greater opportunity or are more inclined to be unionized than adults and that many individuals report having had a unionized job by the age of 25. The authors also find that whereas the stock of unionized workers is largest at middle age, the flow of workers into unionized jobs is greatest between the ages of 16 and 25.