Happy B-Day for Len!

Oh, hey! Look! It's your birthday today!


......................


Yes it is, and now for everyone else to find out her actual age......

Follow my formula:
The date of the very first Melty Blood game which Len has made her mysterous and very cute appearance, minus this year's date, and add the sum of 100 to that number...

The answer to this is her exact age of now!

And as of being a succubus, compared to everyone else's age in the
netherworlds of Disgaea, Phantom Brave, and Makai Kingdom, this is
why she's appearing only as a child; she's very young and has a long
way to go.

Well, actually I think you forgot to factor in Kagetsu Tohya (and Tsukihime, though Len was more of a plot device then) into your formula. Len (and by extension White Len who existed as a part of Len for that amount of time) has been on this Earth for about 400 years. Also, I don't think she would have "a long way to go" because she's an artificially-born succubus created by... that mage who defeated Einnashe (please answer this in my other thread if you know his name), so I don't think she'll grow as time goes on. She's a succubus for the people with... special needs. Also, she and Shiki Nanaya got married! (Also shows her age there)