The complex part of this issue is K cutoff dates. I did not hold my older DD back and wish I did. On the other hand if she had lived in most other areas of the country she would have had to spend another year in preschool. I sent her to college still only 17. What added to the problem was everyone else who was holding their children back. On the other hand my DS could have easily skipped K. And I have seen some very frustrated and bored HS seniors who had been held back.
Personally I think this whole idea that every kid should be learning in lock step according to their age is frustrating. But iif you are going to make age distinctions you should make everyone stick to them because maturity and ability are all over the map.
