in the books he is around 800, and his species lives for about 100 to 150 years
it is also said in the books he stays alive using the force.
also in episode 3, emperor Palpatine says that there is a SITH legend that has someone (I forgot the name) the wise learned to KEEP people alive. he then taught his apprentice, who killed the master in his sleep.
this begs the question, what Says YODA isn't the apprentice?
he did live a looong time till he was killed...
and it was the force that kept him alive, which was a sith trick
Yoda does say “End the Sith, we must.” But, hypothetically, he could have lost against Palpy on purpose. But if he is a Sith, then why does he fight Palpatine in the first place?