A.B.
If your son is developmentally on track, then the Tag reading system is too young for him.
My 5 year old got it a year ago at Christmas (when she was 4 obviously lol) and she loves it but doesn't use it as often as I'd hoped. None of the books go beyond the level of an 8 year old so he may outgrow it far too quickly.
I believe the age group is 4-8 for which it is recommended.
Try a Leapster 2 or a Nintendo DS/DSi with some educational games. The Nintendo will grow with him into the teens.