I graduated high school in 3 1/2 years (my highschool didn't allow less than that regardless of whether you'd met the requirements.) Of course, I graduated early because I was already a mama and needed to be able to work - hopefully not going to be an issue for any of your all's dc! I worked full time and took a couple community college classes during the winter and summer terms before starting full time college in the fall. I know it sounds weird, but I always felt being a mother and going to school helped me keep a good perspective of my priorities and especially in med school helped me be a much more balanced student - sort of like other life experiences help you focus better on college also. I can't say I really recommend teenage single parenting for most kids as a way to develop perspective and priority setting though!
I have a bunch of younger in their class kids. Older ds is Aug 24, making the Sept 1 cut off in IL by 1 week. We had a big debate when he was little - but he was always very verbal and social and his kindergarten screening (we actually had 2 due to worrying about his age) strongly suggested sending him on to K. Interestingly, he thrived in full day kindergarten despite having not had any significant preschool (I took him out as a three year old after 2 mos or so because he was obviously not enjoying it and seemed too young and never got around to sending him back.) He has not had problems that I feel are attributable to his age in school. He has ADHD, but is very bright, and has always had more older friends than younger. Could he be more mature? Yep. But, his older friends seem to struggle in all the same areas and actually of his class group of all the college bound bright kids, he is doing really well comparatively. (His best friend has already dropped out of school twice - in 1 year, another friend didn't even finish out her first semester due to anxiety and homesickness issues, etc. etc. The grade issues he's had that I fretted over so actually were relatively minor compared to some of the issues a lot of his social group has had.) This kid is mister social, though, and has always been a happy and content person.
My next child . . sigh, it remains to be seen. She skipped first grade after an awful year in kindergarten. Academically, she's more than able to do the work in her current grade setting. Maturity and social-wise, she is very mature in some ways, but behind many of her friends in some street wise ways. I'm not sure I view that as a negative, but I think she sometimes does. She does have a close group of friends, but tends to the "misfit" crowd. She's really struggled in middle school, but I can't decide what to attribute to her age and what to attribute to other factors (mostly that infuriating school.) The two things that most influenced me to move her up instead of leaving her in her age group with outside enrichment were how miserable she was working so far beneath her grade level, and the psychologist who evaluated her saying that he felt that she was struggling just as much socially with kids her age as academically - they just weren't compatible, and she was actually happiest in settings where she could be with older kids. She did change schools when she skipped a grade and we've always kept her age as under the radar as possible - and her school environment doesn't seem to socially ostracize bright kids, she actually enjoys being one of the "smart kids" where as I always hated that part. My big plan for her for the next year is to focus on some outside of school stuff to help her realize how big the world is, and how small/insignificant a lot the middle school drama is.
My next kid down is a boy born in late June, so not quite as extreme. He is also very bright (maybe even more so than dd) but was obviously more immature when it was time to start school. He has largely thrived in school, though - especially this year when he had a lovely teacher who really enjoys boys and worked hard on developing his confidence as a speaker and leader. I can't believe the difference in his maturity level this year - maybe just coincidence, but definitely wasn't hurt by a teacher who believed in him so much! He'll be in 5th grade next year, so we'll be heading to middle school soon with him.
I think it's important to be flexible and continously re-evaluate the situation. I wouldn't hesitate to have a child go to college a year late, or take other time off to re-situate if necessary. My mom graduated college at age 53, I got both my bachelor's and professional degrees while parenting - so I tend to think there's no set way you have to do it. I think it's unfortunate, though, that in a lot of ways moving back down is so much less socially acceptable than skipping ahead - makes it hard to say "we'll try one year this way, and if it doesn't work out will go back to the other way."
I think I have to go to bed. I'm so tired. I called to check on my 15 yr old mama, and the nurse says that she has largely spent the whole day nursing her baby - she is so tickled that her baby nurses so well! I wish I could bottle that and sell it.