Average age on an aircraft carrier appears to be 19 [0], 20 [1], and/or 24 [2] years old.

0: https://www.nytimes.com/2008/04/20/arts/television/20jens.ht...

1: https://archive.defense.gov/news/newsarticle.aspx?id=15334

2: https://mashable.com/2016/06/23/what-its-really-like-to-live...