Although I also don't think that it's a very good idea for someone with little experience to own a recently gelded horse, even a well-mannered one (there's always the possibility of something bad happening), I think that if you have your trainer, who is not only experienced, but knows the horse inside and out, I don't think it's that big of a deal. As long as you know the horse, you take the proper measures, you realize what you could be getting into, and you have someone with you to help just in case, if he's a good horse, at least try him out.
I don't know how many other horses you've looked at, but you might want to consider checking out some others, just to see what's there first. This is a really good way to really narrow down your interests and get a better understanding of what you want and are capable of handling. Even if you really like him, I really suggest just looking at some other horses if possible.
If you haven't already, ask your trainer about whether you think it's a good idea, and ask if they'll go with you to look at some other horses. You can always ask to fully commit after he's gelded/ had time to cool off, too- and if in doubt, take your time. If your trainer is in too much of a hurry to sell him, don't worry. There are plenty of very nice horses, don't be afraid to pass him up if it comes down to it.