The Kindergarten Debate

There is a debate over whether kids should start kindergarten at the normal time or wait a year so they will be emotionally ready. Sometimes, being held back has its advantages; it insures a child is ready to learn. However, in the article Delay Kindergarten at your Child's Peril, the authors state that starting kindergarten late can be "less motivated and perform less well". They said that late starters can even have a lower IQ! 
In Malcolm Gladwell's book Outliers, Malcolm says that late starters have an advantage, being older therefore more developed. He relates this to sports, such as hockey. If you are one of the oldest in hockey, you are more developed, appearing bigger(better) than younger players. 
In my opinion, I think a parent should put their child into kindergarten when they think the child is ready. If the child is 5 years old but still haven't really developed mentally enough, the parent could hold them back another year. If a child is 4 and has shown extreme ability, a parent could send them in at that young age. So, I don't really agree with "accumulative advantage" because it's no advantage if a child's at the same mental capability as others; age doesn't really count in school in my opinion.

 This is kind of unrelated, but here's my personal experience:
I started kindergarten at 4, and I think it was actually a little better. I did feel out of place though, since I was always the smallest. Now, being the oldest in my grade, I feel out of place sometimes, too. It is difficult with an August/September birthday, so I think that is a place where parents struggle the most.
Also, I noticed in schools in central U.S and England, the cutoff date is generally August(the oldest kids are in August, a few young kids are in here too). However, on the east coast, the youngest kids are in October and even November, way younger than other places. Maybe it's an east coast thing?