My sister was born in September 2010. She’s going to be in high school this autumn and one of the first freshmen to turn 15 during the school year.
I was 15 years old when I started freshman year and 16 by the end of the year, so I graduated high school at nineteen. (College grad since age 23 last year).
Oldest.
There’s a podcast by Malcolm Gladwell where he says data shows the single best predictor of successful college application or success with college sports is your month of birth. Being oldest in the class comes as a huge advantage and is making many American families “red shirt” their child by putting them in school a year later; and this making them the oldest child in the class all the way through.