I'll chime in that grade retentions late (at or past secondary level) don't appear to be that common among those I know who skipped. I took an extra year in college, and many extra years in graduate school, which I expect had something to do with waiting for social-emotional maturity to catch up, but I don't view those years as wasted, by any means (and I have degrees in diverse fields to go with them). Rather, the early entries and skips provided me with additional time to explore areas of intellectual and personal interest, separate from career preparation. If early entry to uni is not an option, one can still pursue personal interests and explorations during a gap year or two.
I think an inappropriate grade skip--especially one motivated by reasons other than child-driven educational thirst--might be more likely to result in repeated grades later. Or, for some 2e or highly-skewed children. I have one who has been grade advanced twice, and another who hasn't. They are about equally advanced in math, but one is strong in writing, and the other is about age-level in writing, and maybe a little below in spelling. Grade skipping the second one across the board would require a lot of accommodations (which are not an issue, practically speaking, because we homeschool).
