I'll address the Area 51 metrics first, the thresholds published on Area 51 are rather misleading.
We currently are at 14 questions per day, with the official threshold for excellent being 15 questions per day. This is one statistic whith a huge variation between sites, some sites like Skeptics have graduated with a question volume far below the threshold. Other sites can easily hit the threshold at the start of the public beta. Our current volume is easily enough to sustain a healthy site, this is nothing to worry about. More good questions is always nice, but simply more questions wouldn't help us graduate any sooner.
Our answer rate is at 87%, the official threshold for excellent is 90%. This is again a statistic that depends heavily on the site subject. I don't think this is a problem currently, but this is an aspect we can certainly improve on. Biology is a rather broad field, the more difficult or specialized questions can often only be answered by users in the same specialized field. Getting this rate way up is unrealistic.
We have 35 users with 3k+ reputation and 45 users with 2k+ reputation. Those are important threshold because these users will be able to close and edit after graduation. This is a sufficient number to have effective community moderation even at the higher privilege thresholds of a graduated site.
I'm not sure what to make of the answer ratio, I don't see a problem for this site here. I can see how extreme values would be problematic, but I think we're at a reasonable point.
I've put some images of our traffic in comparison to Chemistry, which is a site of a similar age and topic that is about to graduate:
They have a bit more traffic than us recently, but overall we're pretty similar in traffic growth. I think traffic looks pretty healthy and shouldn't be a barrier to graduation.
Herre is also a comparison with Physics, an example for a graduates site with a similar topic:
From the number alone, I'd say that we're ready to graduate. But the numbers alone don't decide this.
A severe quality problem would also prevent graduation, but I don't think we have that here. We could certainly do better, but I think overall quality is good on the site. I'm not entirely happy with the ratio of popular biology questions to more advanced questions, but that is not a barrier to graduation.
One aspect that I think could improve is the community engagement on meta. Our meta was pretty silent most of the time, this has improved significantly recently.
My guess would be that we're ready for graduation, but that either our evalution wasn't scheduled yet or the design bottleneck is the limiting factor. But this is entirely my own speculation, I have no inside information here. It is almost impossible to get a straight answer out of an SE employee on when a site graduates, so I don't actually know what SE thinks in this case.