Children, like adults differ in temperament and working style. There is a standard test in Psychology, where the categories are ‘Impulsive’ and ‘Reflective’. I have not favoured use of the test as I feel that dividing all people into only TWO categories will not be very useful. There is a continuum along which all of us will be found to function. Some children may just be closer to one end of the spectrum than others. In itself, it is not a problem, but it can result in minor glitches because sufficient attention is not paid to details. Perhaps you should start your son on Chess, where he will have to think of his moves and develop patience. Or even model making with Meccano. I think his leisure time is fully taken up with Piano lessons, Taekwondo, etc. Perhaps he needs to have some unscheduled time to read books or play games, where he can initiate the change of activity. Possibly he is rushing through his activities because he wants to do something else. Talk to him and explain why you are concerned. A child who is fast at everything also has a head start, in a manner of speaking. He will also be the best source of information about himself!