User blog comment:B214/Volume 23 discussion blog/@comment-31137559-20170506225314/@comment-29963364-20170507202524

Azazel did say, in vol. 21, that Sirzechs and the rest of the current Satans still practically kids since they "haven't even lived 1,000 years yet."

So we know that Sirzechs and Ajuka (and Serafall & Falbium) are less than 1,000 years old, but older than 500.

This means that a Devil is still considered very young until they reach 1,000 years. So that means that Devils like Zeoticas, Venelana, Lord & Lady Phenex, and other "adult" Devils are over a couple thousand years old.