Board Thread:General Discussion/@comment-45705146-20200509070014/@comment-37883549-20200509115858

Some of the ages we have listed on the Wiki aren't exact. I wouldn't mind placing something like a (presumed) next to it, but I am not sure what Angelo or the other Admins think about this. They might just prefer going with the age that was calculated by this observation (in LN 13) and changing it if a more accurate age is provided later on. Annoyingly enough, Emilia's age was changed in the LN compared to the WN version so we can't use the WN version as canon (she was 107 there)

For what it's worth I checked Re Zeropedia and they list her age as 秘密 (secret).