I agree with most everyone here. Consistant training and handling, being clear with him what's acceptable and what's not right from the get go will help his mind in the right place.
Trained and handled horses behave well most of the time; untrained and unhandled horses misbehave most of the time.
Anything with a thinking brain will sometimes have their ******ed brain fart moments, be it gelding, mare, stallion, or human.
As a yearling, he should have dropped by now, for sure. I really hope you don't have a bi-lateral crypt on your hands. Not that it's horrible per say, but in order to get his nuts out the vet will have to go inside both of his flanks in order to get to them.
The barn I'm working out of right now bought a really nice Shining Spark colt for an inane amount of money, turns out he's a bi-later crypt (meaning neither of his nuts dropped). He's going to be six this year, I believe. They have not opted to geld him, and he's shown absolutely no signs of being studdy at all. In fact, quite the opposite. He's known as the "gay horse" around here. Poor dude. Super nice to ride, though! I'm hoping to get him out to a few reining shows this summer.
Your vet will be the best one to discuss options for this should that be the case.
a stallion is only as good as its handler/rider.
I agree with this 95%. I've seen some really nice minded stallions owed by some the biggest igits out there and still behave themselves nicely. But you're right, though.
No training = no horse. To an extent, of course.