Yeah, my email usage at age 12-15 was also almost nil and that was in the 90s. Doubt stats at 12-15 correlate well to whether those kids will use email when they hit college.
Agreed, I didn't have much use for email at 15, because I interacted with all my classmates and teachers every day; coordinating things was simple, and all my schoolwork was submitted in person. I primarily used email for asking questions on Linux mailing lists, and even that pretty rarely--15 year old me would probably be pretty shocked at my current level of email traffic.