[cperciva]

Canadian here, but I think the US follows the same age-grade mapping. Kids usually enter Kindergarten in September of the calendar year in which they turn 5, i.e. those born January-August are 5 years old and those born September-December are still 4 years old. After that, grades 1-12 follow with a majority of post-secondary-education-bound students entering a few months later.

So yes, in the modal case (advancing with the cohort) a student entering college will start at 17 years old if their birthday is late in the year.