Giftedness cannot be identified unitl the end of third grade, and most early gains that the quick learners have will have disapeard completly by that time, thus the truly gifted children can be idenified with reliable results.
One word of caution. Your son will be one of the oldest in his class, a full year older than some, and while it may seem incocievable to you now, even very bright children who learn quickly can have learning issues. Be aware that his advaced age will not be the criteria that is used to decide if is behnind in any issue, he will be judeged only by grade level for the purposes of intervention, so for you, it is absolutly essential that you act on any indication of an issue as early as you possiby can, so that he gets targeted intervention as soon as his grade level allows, even though it will be a year later than the children who are at typical age/grade. He will not have any time to wait and see if he has an unforeseen Learning disablity, so don't wait on intervention, especially for reading and decoding.
I see this scenearo often as an educational advocate, both kids who were labled as gifted too early and were not really gifted when they started 4th grade, and kids who were held back for kindergarten until age 6 and ended up having an LD but did not qualify for intervention based on what 8 year olds should be able to do because they are being compared to 7 year olds.
I guess I would say that he is doing a lot for a child without kindergarten instruction, but not as much as he would be doing if he had attended Kindergarten last year.
M.