Well, I technically started school early.. than the usual age. Not entirely skipping, but at a very young four... (just turned) went to full fledged kindergarten.
Then we moved after kindergarten, and I was supposed to go to K again due to the cut off date being different in this new district.
My mom pressed, and I wound up in first grade instead of kindergarten. Technically I should have repeated k, but I read at age 2-3, and was doing math, etc... I was in the first grade.
Because of this I was consistently the youngest one my entire school career (even in college). It was fine in the elementary age, but in the higher grades/high school/college, it was a challenge. The challenge started in 5th grade, and continued until I was in college.
I was the last one to get a license, last one to have a birthday, and last one to do many social things. Socially it was rough for me, and it was a challenge being the youngest, smallest, shortest, and it hurt a lot. My social skills lacked as well.
I was academically prepared for most things and school wasn't a struggle until I hit college. Now that I am back in college, I still see it as "fairly easy", even though I am working, and with family.
I had a friend that I dated who skipped most of high school, and went directly to college. (He was a college freshman at 15, graduated at 17!). He was insanely intelligent, but his social skills were well... not truly mature. Super nice guy, but he talked to "impress", and was not truly relatable.. He could tell you the square root of any number, and many math formulas.. but to talk about "normal" everyday stuff was tough.
My DH had a similiar situation.. when he transferred from one school to another, he had enough credits he technically skipped 11th grade.... but this was military school, so his experience is different. He went from 10th grade (military school), to 12th grade (military school)... but this is different situation of course.
I have to say that I hated being the youngest. I even remember telling my mother that I wish I was held back.