This is another argument that "by age" is not the best way to find one's academic or social peers.
Some people in 2nd grade should be in high school. Some people in high school should be in 2nd grade. (And, academically, sometimes that's different by subject; some people need to be in 2nd grade math and high-school reading.)
I was a TA/lab-assistant at the community college I was attending. I spent a lot of time talking to and helping out people, universally older than me, who had gotten out of high school and needed to figure out where in a multi-year curriculum of remedial math they should start.