I understand that the characters story is set now and I don't know much about D:OS 2 yet so this might not be an issue, but now that I have finally finished D:OS I'd like to put this here anyhow for future thought.
Giving characters a unnatural long life span is fine.
The issue is when you make said character playable and need to balance him/her for the sake of gameplay.
Making extremely old characters in fantasy is to make them special, and with it often comes power, wisdom, skill, knowledge etc. Unless you are imprisoned for 500 years you will learn stuff along the way, regardless of your starting point.
If you have a character that has been hunting demons for the last 950 years, you'd think he had picked up quite a few tricks over the years and be somewhat powerful by now. But no, six spells is all he knows and is as "powerful" as any average farmer.
For me at least it kind of ruins the character.
