The question seems simple enough, how old is she? That simply asks how many earth-years have passed since she was born.
As you stated, she was 13-1/2 in 1980 at her first appearance. That was 33 years before 2013.
Kitty Pryde is therefore 33+13-1/2 = 46-1/2 years old as of January 2013.
A different question is "How many years has she lived?"
As @Valorum indicated the individual is The Dark Rider, aka Marauder and Masked Marauder a gestalt being that was formed from a band of mutants called Team America. (They have somehow lost the copyright to that name, or didn't have it.)
The character I was thinking of was Wolf, a member of that team, who channeled The Dark Rider in episode 6 of The New ...
Based on this numbering:
The following appear (links attempt to give best reference for that particular 'look', a + indicates not technically considered a mutant):
Negasonic Teenage Warhead
This was the "Growing up X" by Darqstar, which apparently expanded to the X-S Series.
Darqstar's X-S Series was a popular series about Hank McCoy's adopted daughter, the OC Sikudhani ("Siku") Edna McCoy: "The series that started it all. When Hank meets up with a blue furry baby with no family, what does he do? Adopt her, of course. Well, what would it be ...