Hi
1. First thing, is your current bunny neutered? If not, that needs to be your first step. Then I believe they need 4-6 weeks for their hormones to settle and to heal. As to the age, it doesn’t really matter, but usually people choose to bond with a rabbit of similar age. The crucial thing is that they are both fixed and healthy, regardless of their sex.
2. Yes, most would agree it is possible to bond most rabbits, although some are easier than others. Ideally you could take your bun on some “dates” at a shelter, so see which he gets along with. But, my first bun was bonded with a bun that belonged to my friend (who she could no longer keep), and i used the strategy you describe (separate pens, near each other but not touching). It was a long bonding process (3 months!), but with patience it worked. Is there a specific rabbit you want to adopt? Or is dating just not possible? There is tons of bonding info online, it sounds like you have done a bit of homework on the basics?
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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.