Sorry for your loss of Coconut
Age doesn’t matter really, it’s all about their personalities (as others have said).
Your vet is partially right that not all bunnies will behave normally at speed dates, but they can help you rule out bunnies that will definitely NOT work (some bunnies just do not like each other!).
It can be nice to try to match ages, but you never really know how long they will be with us (even with the best care, things can happen beyond our control), so unless the gap is huge, I wouldn’t stress about it. If you fall in love with a senior bun and your bun gets along with him/her… then you might decide to go for it. (I’m biased though, I recently adopted a 9 year old bunny man and wouldn’t trade him for all the 1 year olds in the world because he is such a sweetheart).
You might go to the shelter and meet the buns that are available, and pick out 2 or 3 that you might like to adopt. Then when you bring in your bun, you can have Peanut meet those buns. If none seem compatible, then you can bring her in another time when there are more eligible suitors.
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.