I have to say, I think this is a genetic thing, and our boys sire is of National standing, and so of course, he wasn't gelded, and our boys, who are both now full stallions live happily together... They have the best temperment and both of our little daughters feed and groom and love on the boys. I understand from people who kept their sire, that he was quite the gentleman. The boys sire was kept with the boys without incident. They are three year olds.
I have to say (as I put on my flame suit here) from what I've seen in my very novice experience the temperment has so much to do with feeding and many other outside influences. Our now gelding was in with seven other stallions until he was four years old, and he had to fight for his feed. Heck, he wasn't safe with anyone, because he was taught he had to fight to eat, and fight he did. One man DIED (of a heart attack) while trying to train him to be able to be handled. Someone on this website figured out what his attitude was all about, and as soon as we started feeding him in a stall vs outside, he calmed way down. I regret that we had him gelded. We thought gelding would make him safer around the kids... well... six mos later and NOT! However, today, he's a pussy cat. He realizes that he has his feeding spot, where other horses will not be, and he can spend all day eating if he wants, and often does. He'll take a bite of grain, and then a bite of hay... and two hours later, he's still in his little barn .. munching. We did not see any change in him until we met his needs as far as him feeling secure. Gelding did nothing for him. Even our vet said that gelding takes the edge off, but if you have a naturally agressive horse sometime even gelding doesn't help. All testosterone is NOT produced just in the testies..... (I learned that here too!)
Our Horsezilla is now saddle broke and does church affairs etc, with many many children with no riding background. He is always the gentleman ... NOW.
My opinion is, that you have to judge whether or not your colt demonstrates any aggressive tendencies and then make the decision to geld or not to geld. If after you geld, you might even decide that he still has agressive tendencies and that he just isn't safe around children. Our kids got no where near our Horsezilla until he and I had dealt with his issues. I believe it was a combination of raging hormones , fear of not getting fed, plus he had a horrible case of thrush when we got him. But now.. he's the sweetest horse you'd ever meet.
Don't feel pressured to geld or not too. You will know in your heart, when the time is right. Also, check the Farmer's Almanac for the best days to geld... (I know we did it in March which is what they reccomended that year).
God Bless...
JMHO...
Lynn W