Our (neighborhood public) school put full grade acceleration on the table for our dd at some point, and we passed it up. Reasons:

- being a twin complicates the decision. Skip only one? Skip both?
- maturity level was not advanced
- one year grade acceleration wouldn't have solved the academic mismatch problem
- more time before college to explore other interests
- more time for us parents to spend with kiddos before they go off to college

Back in the day, I went to an uber-elite private college. I knew a number of 14/15/16 year olds as class/dormmates there, and felt their experiences were not optimal. The kids I knew who were closer to the average age of their classmates but had a head start on the curriculum seemed to fare better on average.