I am relatively inexperienced on this board, so you should listen to other posters more than me :-) but I'd say yes.
My DS10 taught himself to read at 3, was reading well at 4, etc. Super into science and could discuss science knowledgeably early. All that kind of thing. DD8 did not "really" learn to read until she was around 6 or 7. Very typical timeline - although she took off once she was confident (she's perfectionistic, and would not admit what she did know until she was sure of it). She was just tested due to behavior issues this year in school (2nd grade) and low and behold, she tests higher than her brother, despite not showing real signs of being anything beyond an accelerated learner/high achiever until this year - and even then it was hard to tell b/c she wasn't actually doing much work (absolute refusal to do the menial tasks she had in front of her... in talking with the school psychologist, it turns out she met all the benchmarks/had mastered 2nd grade curriculum goals in September.. of course no one bothered to tell me anything beyond "she did well"... sigh).
If you can test him now, do so. The testing allows me to say w/out a doubt that DD deserves to be subject accelerated, and advocate for her w/out seeming like "that parent" who thinks their kid is "extraordinarily gifted" (but really is just smart...).
I wish I could give my kids back the years they spent learning very little in school. DS especially seems to have lost the joy in learning he used to have. If I had known what I know now, I'd have done it when DS started 1st grade for sure.
