How old is the term denden?

I am a student of Japanese history as well as a hobby fiction writer (although I am in Japanese 202, so I know a decent amount of the language). I mainly study the Meiji and Taisho Eras, and am currently setting a story in that time period (1921-23). There is a British character who's name is Draethen (yes, its supposed to be almost painfully British) and he is close to some of the Japanese characters.

As a result, his nickname is ''でれくん.'' I know that the pop cultural use of ''でれでれ'' within terms like つんでれ is very recent, but I can't find out how old the term itself is.

The reason I'm asking is primarily because ''でれくん'' is a perfect nickname for this character, as ''でれでれ'' means ''exhausted'' and ''lovestruck'' and he has a chronic illness that makes him tired, and occasionally women fall in love with him through the short-stories he writes (this wasn't on purpose, I only realized it after I found his name).

I was mainly wondering if it would be something that the other characters at the time would realize was a pun or not. If not then it's just funny to modern readers, but if so, I'll have someone mention it.

Also, slightly unrelated, but Google Translate lists ''でれでれ'' as an adjective, does anyone know if it is a -い or　-な adjective?

Thank you so much!

I don't know anything about that.
But for reference, I googled...

on Meiji 22,
酒などを呑んでれちやあゐやあしないよ
from 月梅薫朧夜(tsuki no ume kaoru obooroyo, Kabuki; 1889) by 河竹黙阿弥(Kawatake Mokuami; 1816-1893)
http://ja.wikipedia.org/wiki/%E8%8A%B1%E4%BA%95%E3%81%8A%E6%A2%85

on Meiji 35,
芸妓のでれつく塩梅が余り鼻持もならぬから
from 社会百面相(1902) by 内田魯庵(Uchida Roan; 1868-1929)
文學者及び文學志願者は思切て女に惚れるべし女にデレるべし
from 不明 by 内田魯庵
http://ja.wikipedia.org/wiki/%E5%86%85%E7%94%B0%E9%AD%AF%E5%BA%B5

correction: 酒などを呑んで でれちやあゐやあしないよ

でれでれな人を見た (I watched a exhausted man.)
It's -な adjective.

BTW, there was a word "でれ助"(deresuke) means "a exhausted/stupid man".
I think "でれくん" is a good pun that's a bit gentlemanly paraphrase of "でれ助" suitable for Meiji era.

The term here is "deredere," not "denden," I guess.

Te guy's name is Draethen, so apparently they shortened it (changed the sound slightly on top of it) and added "-kun" as a friendly ending normally used for guys.

I don't know if people at the time would have considered a pun or just a shortened nickname.

"Deredere" is an adjective in the sense it describes a person's condition (not standing straight up, either lovestruck or very tired), but it is normally used as:
でれでれしている (is acting/being lovestruck/exhausted)
でれでれした態度 (an attitude that is...)
and is not really considered i- or na-adjective on its own.