The question is: Has it been confirmed that the little girl IS X-23?

She's not going to age up that fast because of her healing factor. She'll look young for around 120 years. She'll mostly a look like a teen until then. Besides, Fox has already made their choice of actress'.
They need to start young and they are in fact going to do that. This is because they want to use the X-23 character for about a decade. You are right in that it's nothing new to see an adult play a teenager. But not all of them can do it, and for as long as Fox would need. Especially for 10+ years. Tatiana would be 40 still trying to look like a 16-17 year old. It just wouldn't work. She's already getting to her cougar phase IMO.

Well, she'll eventually age up right? If Logan can get old and she's his clone, why can't she get older also?
And adults playing teenagers is nothing new. Natalie Dormer plays Margeary Tyrell in GoT and she's 34, while her character on the show can't be older than 19/20. (In the book I believe Margeary is only 16).
I'm 60 - I won't be a sexagenerian for a year!

• cowabunga44

X-23 IS a "kid." Her hook is that she is a child soldier type! She has never been depicted as being above the age of 18. Even now she is a "kid" in the comics.
I blame the horny comic book artists for drawing her the way that they did at that young.
I don't know WTF they were smoking back then. She also joins X-Force when she's 16 if I remember correctly Domino mentions her age during the Kyle & Yost X-force run.
13 When she escapes the facility.
14 when she meets Logan. and her stint as a prostitute. (Horrible I know!)
15 when she joins the X-men.
16 When she joins X-Force.
16 during her first solo series.
As of All new X-men and All new Wolverine. She's still confirmed to be a teenaged girl. So most likely 16-17.
Tatiana Maslany is in her 30's or something right? She cannot believably play a teenaged character at this point in her life. She's beautiful yes, but she missed that chance by a decade. Even Tim Miller loves the idea of Deadpool getting his natural ass handed to him by a bad ass little girl.
Hailee Steinfeld was already fan casted, but that's just a fan cast. I suspect Fox already knows who they want to go with!