Yes, it happens. Often it's not 2 years at once but staggered from elementary to middle school or a gap year to college.
darn, then you add in a redshirt or transfer and you graduate at 25.
Lyle Thompson was 20 years old as a freshman.
Shoot, you can get to that with just being a single holdback and a Sept/Oct Bday. I am guessing a lot of Canadians in D1 are 20 year old freshmen.
2x holdback with Sept bday would be 21 as a freshman going against a spring Bday freshman that hasnt been held back who would be 17 for a semester. That's why some parents do it.