My 11yo August baby did fine in the earlier years (nursery, kinder, first years of primary) but not so well there after.
It started to feel like he was trying to fit windows in a house that had lumps, bumps and holes in the foundation.
Two years HE sorted out the foundation, but I noticed that concepts "clicking" for him happened a good six to 12 months after they were introduced, lots of revisiting notwithstanding.
He is back in school, but for reasons more complicated than his borthday it is not going well, so next year he is going to Inter High and we'll put him back a year and let him float up a year group if and when needed.
I think being one of them youngest can be A factor to watch out for, but as others have pointed put being one of the oldest is ot wothout its pote tial pitfalls either. And any issues are probably more multifaceted than just age alone when you look at any individual child.