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As the wiki states he was aged 9 years old when he was turned. Just like all vampires, they do not age beyond what age they were when turned. For all we know he could be beyond age of all vampires including Russell(2800 years old), Eric(1100+), and especially Bill(176). This detail has not been made known yet, however but we can assume he is a very old ...

The reason is that Sookie either knows or assumes that Tara is too far gone or would be dead before the blood could take affect. This is backed up by a couple of points in the series that is takes a while for the blood to work, and more than a bit is needed. Sookie knows of Tara's dealing with vampires, but I assume her desire to save her childhood friend ...