Not to be too pushy here , but I did want to say, as a parent who is pretty far into this journey, that not all of us feel that the repercussions become worse later on down the line. I did hear that from the principal @ the elementary where dds started school -- that the maturity differences, etc. would be greater later and I wouldn't know that yet in K. My oldest is a freshman in high school, so we are at the point where we're seeing college in the near future. I will admit that my oldest is somewhat of a special circumstance. She has both a fall bd & she skipped the last year of elementary so she is not quite 13 yet. We're looking at her heading off to college at 16 (nearly 17) but it is absolutely the right decision for her socially as much as academically.
My youngest has a later fall bd than her sister and is a different kid. She's not one whose going to be skipping grades, but she still is good as the youngest in grade. I don't regret starting either of them when we did and I don't see maturity lagging behind their grade peers even as we're into middle and high school. FWIW, I went off to college just shy of 18 and don't feel that being a year older would have been any benefit for me either. There are a lot of other things that might have made a big difference in my experience in college, but age isn't likely one of them.