It is time to geld the colt. He is no more likely to be proud cut at this age or any other age. Just get a vet that knows how to geld a horse.
I totally agree with the other posters about not getting an untrained horse. You would be way better off with a mature, well trained animal. My first horse was untrained, and she almost killed me on more than one occasion. She eventually became a nice horse because I had a trainer help me with her. I do not recommend that anybody without experience buy an untrained horse. With all the nice horses that are looking for homes, you should be able to get a well trained horse for a reasonable price.