Here’s what the House Rabbit Society has to say about it:
From the article about spaying and neutering: http://www.rabbit.org/faq/sections/…ml#too-old
When is a rabbit too old to be spayed or neutered?
veterinarians will have their own opinions on this, but in general, after a rabbit is 6 years old, anesthetics and surgery become more risky.
It is always a good idea, in a rabbit over 2 years of age, to have a very thorough health check done, including full blood work. This may be more expensive than the surgery, but it will help detect any condition that could make the surgery more risky. This is especially important if anesthetics other than isofluorene are used.
But obviously some vets feel comfortable doing it later in a bunny’s life. It may be because more and more vets out there are racking on years of experienced and are skilled enough to know when an older rabbit will be healthy enough for a spay/neuter.