Ollie is also among the many, my vet is of the few who don't go in guns blazing, it is very low and easy to locate.
He felt there was no need for op.
Now when he was 7 months we got him from a rescue, only one I have every heard of who let dogs re home with out castration
when I went to vet it was same as you, I was horrified, I explained that as only had him few weeks it was the last thing I wanted and would wait a while - next time I went a different vet said no rush and the 5-6 year top limit advice.
When we moved to new vet, who is a small 2 person vets team, he said it was almost in right place and to leave if we wanted.
I think if it was not easy to find I would have had it removed before he got too old.
£800 does seem steep, I have been told that if they need an op should be done by 5 -6 years age.
I think the fact she the vet is reviewing in 4 weeks is putting an increased worry on to you. Please to not worry - and rush - as others have said he is still very young. I certainly would not have such a young dog operated on unless needed, is this vet only one in practice or are there others, I would go to another vet in practice and say you have been very concerned and worried at what seems to be urgency. It is uncalled for.