What differentiates the Valar from the Maiar?

[Puddleglum]

Originally Posted by TheLostPilgrim

Also, were the Maiar as old as the Valar--did all the Ainur come into being at the same time

The Valaquenta notes that Melkor "was coeval with Manwe". The word "coeval" means of the same age indicating that Manwe & Melkor were created at the same time.

It's not absolute, but this suggests that the Ainur were not all created at the same time (else, what is the point of highlighting that two in particular WERE?). The Ainulindale only says that Eru made the Ainur "before aught else was made" - not that he made them all in the same instant.

While many Ainu entered into Ea, the Valaquenta notes "The Great among these spirits the Elves name the Valar, the Powers of Arda"
and
"With the Valar came other spirits ... of the same order as the Valar but of less degree. These are the Maiar..."