So, boarding situation. 

A new boarder just brought in a 9 month old percheron stud colt. 

I have a mare. 

The stall he's is wood till about 3 1/2 feet then bars probably to about 6 feet. He is stalled right next to my mare. She is 19 and I have no intention of breeding her. He seems pretty quiet. But I am not happy. 

The barn owner is reassuring me that nothing is going to happen. 

The horse owner claims he spoke with a vet, sent the vet a picture and the vet said "he's not ready to geld."

Im looking for other places to go but my area is scarce when it comes to boarding options. The BO is claiming I shouldn't be mad and all will be fine and is literally begging me to stay.

Am I right to be ****ed?

I really wouldn't worry about it, the most they can do with each other is bicker at each other. You have no breeding risk. I kept a stud at a boarding barn with just 5 foot pony walls between stalls until he was 2. With mares on each side, nobody ever bothered anyone. Where I'm at now we have studs next to mares, everyone is fine.

And with the gelding he's probably right, most vets like the balls to be dropped before gelding & he may not be fully dropped yet. 

What they said.

I would say have the owner reach up under there and grab hold. Anything big enough to grab is big enough to cut. This is my personal opinion but I like my geldings to have a little more of a feminine look and not look like a cut stud. We do that as early as possible. I have had a couple that were exceptionally bred boys that we had planned on leaving stallions. One just got carried away by the girls and tried to jump out of the round pen. The next week he had a sex change. The other one's offense was he just could not pay attention to his barrel training. Nothing major just couldn't stay focused brain surgery fixed that. One last thought, I had friends whose mate started showing signs in the spring that she was carrying a goal. The ONLY time she was near a stallion was when she was on the walker with their stallion. If they decide they are going to have relations, being next to each other in stalls is no problema!  I suggest you get the owner to feel under there and get that taken care of ASAP.