N’s background is hard to place, but I would make a case for N having been born in the early 1800s.
(Under the cut, because this got long.)
Summary
The languages don’t really narrow it down (unless they are really, really old), because they know hieroglyphics and Old English and Latin. This suggests being very old, but they are “an enthusiastic learner” and may have learned these either (a) for fun or (b) from an even older supernatural being. Plus I feel like it said somewhere on the Tumblr that vampires aren’t exactly immortal. (List of languages N knows.)
However, assuming their choice in music says anything about their birth time, then we can extrapolate from there. The era of Classical music lasted from 1600 (Baroque) to 1910 (Romantic). That’s a three-hundred year period, but it’s possible to shave off a few decades. In this post, Sera said that N couldn’t drive a car or a boat (or even a bike), but was an excellent horse rider and sailor. This means that motorized boats and cars likely weren’t invented during their formative years–thus making motorized vehicles an alien concept.* The first car was invented in 1885 by Karl Benz in Germany. Now, if we figure that N was at least, say 30 human years (enough time to be used to not having these things), they would have been born in the mid-1800s or earlier. Bikes were invented in 1817.
Sera says here that N enjoys mysteries, poetry, and the classics. So, poetry was big in the Romantic era (1780-1910), and mystery was invented in the 19th century by Edgar Allen Poe. A lot of classics were also written in this period: Pride and Prejudice (1813); Jane Eyre (1847); Wuthering Heights (1847); Moby Dick (1851); War and Peace (1877); and Frankenstein (1818). This one’s a bit weak, but as all three of these genres had a boom/were invented in this era, I think it can be counted as evidence.
An ask about lingerie shows that N perfers lacy corsets. Corsets were invented in the 19th century, and if they came of age during that time, it would be what they were used to–particularly Nat.
And lastly, their general mannerisms. While Sera says they know what they’re doing with romantic gestures, etc., they do get flustered at PDA, which was highly frowned upon in the 19th century. They are ridiculously polite, even when they want to curse somebody out. Also, they just kind of come off as very prim and proper.
*“Anything invented after you’re 35 is against the natural order of things.” – Douglas Adams
tl;dr I think N is a Victorian and spent way too much time on Google.