Just a fun thought I had.
Nyx, the Dark Mage cursed with eternal youth, often talks about her age; how she's old and experienced, etc. The way she says some things makes it sound like she's been alive for a century or something.
But, it just occured to me the other day that Nyx can have children. This means before the curse took effect, Nyx had already started to go through puberty, so she was at least 10 years old. However, women have a limited number of ova that will actually be ovulated (around 300 to 400); then they go through menopause, which usually happens at around age 45 to 55.
This means Nyx is at most in her early 50s, and has been cursed for at most 45 years. It's still a pretty long time, but honestly the way she talks makes me think she's been alive for a lot longer...