Looking back on we had a mixed experience with acceleration.

The first acceleration was to skip 2nd grade and that went really well. My son fit in well with his 3rd grade class and the age difference was just a non-event. He also subject accelerated in math. He is 2E (he is dysgraphic with ADHD) and ultimately we did send him to a private school, for the ADHD issues not the GT issues (the public school had handled the gifted end of things well). We weren't worried about the high school sports issues since he was very non-athletic at least for anything that was organized school sports. (He ended up doing karate and is a black belt, but like many things he has done his class is mixed age and what grade he is in doesn't matter).

He ended up having a fairly non-traditional school experience with doing a combination of public school, private therapeutic school, private non-therapeutic school which used a public distance learning program.

People always wonder about the social issues. My son was actually shorter for his age and was always very thin (he is still around the 5th percentile in weight). The social issues do exist and were probably the most difficult when he was, say, 14 and a junior in high school. It was a small private school and classes were mixed age but I think he felt that he stuck out as being different.

However, he also said that he wouldn't want to have not been accelerated either. So the age difference making him feel like he was different was a negative for him but not such a big one that he would have wanted to do anything different.

He started community college at 16 and immediately felt at home in that environment. He feels that the social issues entirely went away and that no one cares about his age. (We felt he was not old enough to go away to college at 16 so started him at community college for a couple of years which has gone really well).