I don’t remember where I read this statement, but someone on the internet said that if an anime or web-novel character refers to themself `ボク` in katakana they are probably a boyish girl. 
I should say that I'm steel at the beginning of my journey in Japanese language and surely missing a lot of nuances. 

So I recently started reading my first web-novel (悪役令嬢の兄に転生しました) and I’m really confused with gender of one character named Tirunoa. They are a magic teacher that refers to themself `ボク` and almost every sentence end with `ね～`.
And because of `ね～` it seems more like childish than boyish.

> 「ボクとカイン様の仲だもの。さて、今日から君も魔法やるんだよね。張り切ってやってこーね！」

> 「イル君！イル君！イル君は初期の初期からね！ボクねぇ～、このねぇ～、魔法出来ない子が出来るようになる瞬間！ってのを見るのが大好きでねぇ～。魔法の家庭教師もっとやりたいんだけどねぇ～。面接で落ちちゃうんだよねぇ～。また新しい子教えられるの嬉しいなぁ～。カイン様は優秀過ぎてもうつまんないんだよねぇ～。カイン様もねぇ、最初に魔法使えた瞬間はねぇ、飛び跳ねて喜んで可愛かったんだけどねぇ。もう、勝手に本読んで勝手に使えるようになっちゃうしねぇ。つまんないねぇ。さっ！じゃあまずは自分の魔力を感じるところから始めよっか！手ぇ握ろっ！ね！」

Later it is said that they grabbed their 12 years old disciple, lifted him up and spun around.

> 部屋に入れてもらい、紳士の礼を取ろうとしたカインにティルノーアは飛びついて頭をなでくりまわしてきた。その後、腰を掴まれて持ち上げられるとぐるぐると回転させた後にソファに落っことされた。

I doubt that as a woman they can lift 12 years old boy. At the same time, it would be no surprise if they actually can just because it’s a Japanese web-novel. Can someone tell me what I'm missing to understand their gender? What should I pay attention to?

UPD. I found manga and exactly chapter with this teacher but somehow it confused me even more than web-novel.
[![Teacher Tirunoa][1]][1]


  [1]: https://i.sstatic.net/xgjSn.jpg