How is it possible for Alexander to become a chancellor of the Vampire authority?

As the wiki states, Alexander 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 vampire, if not, very experienced to be on the council.