In thinking over my reply another thought occurred to me. It may be that your child is simply very lively and always will be. If that is his nature it hardly matters if he is held back or kept where he is.
In some countries they have the boys start school one year later than the girls. This sounds like a wise arrangement. I have children of both sexes and lots of nieces and nephews. From what I observe within the family boys mature a little later. You might wait a little to see if your son settles down (or is at least as settled as the other boys). If he is still out of sync you might want to keep him back a year. I do think that age four is young for reading and writing. It is not that the children are not capable, but rather that they do not have the attention span.
The problem is that your son would either be one of the oldest kids in nursery level or one of the youngest in kinder. Most of the time (especially with boys) its better to be older. His placement was based on his intelligence and he sounds like he is pretty intelligent. However, that is simply an easy tool to use for placement and has nothing to do with readiness. If he continues the progression he is in now, he will always be the youngest in his class. Unless he is a genius, this will cause academic problems later on. I would suggest you try a trial placement at the younger level and see how he responds. Is actions at home seem pretty natural for a boy of this age. In fact from now till he is about 7 or so, he will be a very interesting handful. Love him and enjoy him while he is at this age because it is really a very special one. Take a lot of pictures. They grow up too fast.
I would say that children between 3 and 5 are all at different developmental levels. Some may be able to grasp the academics but be immature in the behavior areas. Your son sounds like he could benefit from another year at the nurser level. Since it is 3 to 4, he still fits the cut off. Just my opinion. In the US, kindergarten starts at age 5 to 6 for most kids. They stress that a child must be developmentally mature enough for school and that this is more important than all the ABC/123 they can do. This is just my thought on it. I live in a different country than you and so I do not know how things are done where you are. But another year could make the difference for your son. Good luck.