So, regarding the Fae lifespan...

How does Maas regard immortality? Are they truly immortal in the sense of "live forever, but not invincible" or in the sense of "long lifespan".

How do they age? Are there different species of Fae that age differently? Do they reach a certain age and physically stop aging, or slow down?

There's not a lot of evidence talked about regarding how this world ages, and in the book the word immortal is thrown around left and right, so I'm just trying to get a deeper understanding, if anyone has any information from interviews or anything.