A FSIQ of 121 is generally considered mildly gifted, I would say. His scores in fluid reasoning and visual-spatial processing are really good.
The primary issue is that testing on children that young is very, very volatile - they may score all over the place. Most people on this board will, for that reason, recommend waiting until school aged 5/6 to test.
As for ADHD, I'd be caution of labeling him at his age. Recommendations from my DS' psychiatrist and therapist (my DS8 has ADHD) are - very limited screen time, plenty of outdoor time each day, give 1-step instructions as opposed to multi-step, visual queues (a printed picture schedule) are very helpful.
If your child really does have ADHD, you can't really "fix" it, or even "improve" it on your own. You can, however, make life easier for him, by understanding that his executive function skills are behind the curve and give him extra assistance in terms of planning and organizing his time. One thing that you'll see recommended on ADHD boards and websites is fish oil. I'm not sure there are any studies that really prove it helps, but it sure doesn't hurt to give a fish oil supplement, and I personally thing it helps my son a little.
