DC20 and DC17 were accelerated, though not what I'd consider radically accelerated (2-3 grades in some subjects). It was pretty easy logistically, as their schools offered accelerated courses for a good chunk of their classes, and they enjoyed challenge without doing things too differently than their classmates.
When I was accelerated, my experiences with older kids were quite positive (8th grade humanities while in 2nd, later radically accelerated to college for math and science in middle school/high school). I could keep some of the age-peer friends for recess and lunch but learn with students who appreciated and shared my academic interests. However, some age-minimum laws and logistics made this challenging and infeasible at times (field trips, admission to local academic programs for students my non-accelerated grade or my accelerated grade, sports, financial aid for college courses during middle school...).
Overall, though, it was much better than being left at grade level in every subject or ending up in college full-time as a very young student. It allowed me to learn and experience some of the "rites of passage," like high school athletics, dating, and homecoming (insert whatever social or athletic passions may apply).
