Every planet would have their own rules for elections, including the legal age to vote. This would depend on what age each species felt that its citizens were responsible and mature enough to make the decision on who to vote for. As I said in the previous thread, that would be completely different for long-lived species (such as the Rhaandarite) that it is for Humans.
Agreed -- though, as we both noted in the previous thread, the hard part isn't letting, say, Rhaandar and Earth set their own laws or when a Rhaandarite and a Human reach the age of majority. The hard part is, what do you do with Rhaandarites who live on Earth and Humans who live on Rhaandar?