"Among 17- to 24-year-olds, just over 10 percent have completed college or achieved an advanced degree." Why would we expect 17 to 21 year olds to have complet

"Among 17- to 24-year-olds, just over 10 percent have completed college or achieved an advanced degree." Why would we expect 17 to 21 year olds to have completed college? The common trajectory is to complete your degree by 22, 4 years after high school.