For young children, crazy is actually pretty normal. I'll bet I could put that on kid-size t-shirts and make a fortune.
Well, it certainly isn't too young for you to notice that he's a little "more" than the typical 4-year-old. And you should use that to help guide your decisions about what activites you want to him to do and what kind of daycare provider and school you'll want to enroll him in. Kids that lean to the ADD/ADHD side of the spectrum are often happy when they get plenty of time outdoors (hence the expression "Nature Deficit Disorder" - some ADD/ADHD kids miraculously recover once they get outdoors and spend time climbing trees and rolling down hills). And some ADD/ADHD kids can handle having more outside activities than the average kid, they may not get as easily overwhelmed when you "keep 'em busy." Depends on the kid, though.
If you suspect he's more hyper than his peers, he may have a difficult time adapting to a very structured classroom. My kid is a bit like that, and I found a school that has a child-centered curriculum (i.e. they give kids lot of choices about the kinds of things they want to learn about) and PLENTY of time outdoors, some structured, some freeplay. You may not have many choices, but maybe when he starts school you can talk to the principal about his learning style and it may help him/her place him with the most appropriate teacher. (Hopefully a talented one that can creatively redirect his energies, skillfully harness his need for stimulation, rather than just try to break his spirit by focusing too much on compliance or obedience, or lack thereof.)
One person suggested that her granddaughter will be pushed to start kindergarten a little early. But you may want to consider going the other way. When my son was 4 and in preschool, he was always the youngest (and BY FAR the shortest) kid in the class, and he was sometimes not "internalizing the classroom expectations" (according to the principal). Not "misbehaving", just not remembering the routine, and having difficulties completing tasks independently if he had no interest in them. ("Well, yeah. Is that really unusual? For 4? I often find it difficult as an adult!") His two best friends were on the other side of the cutoff, so I suggested holding him back in preschool one more year to give him a little more time to mature. The teachers, principal, my husband all said no, he's too smart, he'll get bored, etc. (I don't want to sound smug, but the kid is "smarter than the average bear", to quote Yogi Bear). But being smart and acting mature
But once he was in kindergarten, he had a real hard time. Not because of any of the "academic" parts (to the extent that kindergarten is "academic"), but because he had a difficult time sitting still and listening to the teacher unless it was something he was very interested in. (When the mobile science lab visited, they had his rapt attention.) So even though he's plenty smart, I decided to have him repeat kindergarten, although I had
to be more assertive than I had been the year before. I had to have a few conversations with the teacher and principal on the best way to do it so he wouldn't get bored. (Like giving him extra responsibilities to challenge him, rather than just "more of the same" work.)
Another thing that has helped is that I found a wonderful kid's Aikido program. (Don't know your location, but the Roswell Budokan, north of Atlanta, is great for kids.) It's a nice balance of actiivity and having to practice sitting still and listening to the sensai. And it helped him tremendously when he had to sit still through wedding ceremony last month. He was surrounded by his classmates (the teacher was the bride) and he decided on his own to sit in "sezai position", (the one they use in class when the kids are supposed to watch the next technique). He had amazing self-control throughout the ceremony. I KNOW that was the Aikido.
So, carefully choose activities, make sure he gets lots of activities, especially outdoors and interacting with nature, plenty of rest, good nutrition, and careful selection of schools. (Or at least good communication with teachers and principals).
My cousin's son has also had some issues, and they diagnosed/labeled/possibly mislabeled him before he even started kindergarten, around age 4, although I've never seen him act unusually rambunctious. (More than what is "typical", but still well within "normal"). They went the medication route, and maybe it's for the best, but whenever I see him, he just looks like he's stoned. My sister and even my 13-year-old niece think so, too.
It's actually a little disturbing, so I'm trying everything I can to avoid having to go the medication route, including repeating a grade.
I can forward you some information via a private message with some recommendations for doctors or specialists that may be able to help, too. Not necessarily medicate, but to recommend strategies to help him succeed.