Hedcanon.
http://stephaniebrown.wikia.com/wiki/Profile
http://stephaniebrown.wikia.com/wiki/Tim_Drake
Also, Steph is 5'5" (according to most recent reference materials), and Tim is in some versions also that tall. He's also been 5'6", and many other heights. The 2016 DC Comics Encyclopdia does say that Batman Beyond Tim Drake is 6 feet tall, which matches Bat-Tim from A Lonely Place of Living, so your "still growing" point is fair.
Still maintain that Steph should be taller. Just because it's funny.
"We're the same thing, you and I. We're both lies that eventually became the truth." Lara Notsil, Star Wars: X-Wing: Solo Command, Aaron Allston
"All that is not eternal is eternally out of date." C. S. Lewis, The Four Loves
"There's room in our line of work for hope, too." Stephanie Brown
Stephanie Brown Wiki, My Batman Universe Reviews, Stephanie Brown Discord
"We're the same thing, you and I. We're both lies that eventually became the truth." Lara Notsil, Star Wars: X-Wing: Solo Command, Aaron Allston
"All that is not eternal is eternally out of date." C. S. Lewis, The Four Loves
"There's room in our line of work for hope, too." Stephanie Brown
Stephanie Brown Wiki, My Batman Universe Reviews, Stephanie Brown Discord
"We're the same thing, you and I. We're both lies that eventually became the truth." Lara Notsil, Star Wars: X-Wing: Solo Command, Aaron Allston
"All that is not eternal is eternally out of date." C. S. Lewis, The Four Loves
"There's room in our line of work for hope, too." Stephanie Brown
Stephanie Brown Wiki, My Batman Universe Reviews, Stephanie Brown Discord
It's funny, though - I was chatting with one of my fellow reviewers on twitter, and she said that her headcanon is that Tim is actually older than Jason. She knows it's not actually what DC is publishing, but it's all based on an attempt to figure out everyone's ages according to how long Dick was Robin, etc.
What's really silly is the way artists use height as age shorthand. I know it's effective, but it's kinda silly to have the Robins stairstep just to show that they are in age order. I shudder to think what the Batgirls are supposed to look like if their heights are their ages.
"We're the same thing, you and I. We're both lies that eventually became the truth." Lara Notsil, Star Wars: X-Wing: Solo Command, Aaron Allston
"All that is not eternal is eternally out of date." C. S. Lewis, The Four Loves
"There's room in our line of work for hope, too." Stephanie Brown
Stephanie Brown Wiki, My Batman Universe Reviews, Stephanie Brown Discord
My personal understanding of the Tiny Trio's ages are:
Steph is 17 (as stated in Batman Eternal)
Tim is 16 (as stated in Batman and Robin Eternal)
Cass is...somewhere around there (as stated vaguely in Batman and Robin Eternal). I personally wish she were still about Steph's age or a little older, but I currently think she's about 16, the same age as Tim, because she was affected by Mother's gas attack, which was age restricted, while Steph didn't seem to be, though that could be because of Steph's gas mask - which is annoyingly inconsistent in how it's drawn and what it can do. (Also, no one seemed to explain how Damian wasn't affected by that, but eh. Whatevs.)
"We're the same thing, you and I. We're both lies that eventually became the truth." Lara Notsil, Star Wars: X-Wing: Solo Command, Aaron Allston
"All that is not eternal is eternally out of date." C. S. Lewis, The Four Loves
"There's room in our line of work for hope, too." Stephanie Brown
Stephanie Brown Wiki, My Batman Universe Reviews, Stephanie Brown Discord
Well hopefully that stops seeming weird to you sooner rather than later.
Where I live, it isn't unusual at all to see. Mind you, where I live, cisgender people are the minority.
It's quite ridiculous. And yet the most recent DC Encyclopedia still has her listed as 5'5".
If I had faith in Tynion on this end, I'd say he wasn't just doing this to have the short master martial artist trope/cilche, and that he actually had something up his sleeve a la Fullmetal Alchemist; have her get taller as she accepts herself more as a person and less as a weapon, that kind of thing.
I really don't know how much control Tynion has over heights and stuff. He's very enthusiastic about how much control his artists have - so if I had to guess, I'd say that Barrows was like, "CASS IS TINY NOW," and Tynion was like, "Um, okay," and then everyone who followed had to go with Barrows's template.
Things that must have happened...
(Also, Barrows also said, "THIS MASK IS STUPID FOR STEPH, SHE'S LEAVING IT OFF IN THIS SCENE." A lot. )
"We're the same thing, you and I. We're both lies that eventually became the truth." Lara Notsil, Star Wars: X-Wing: Solo Command, Aaron Allston
"All that is not eternal is eternally out of date." C. S. Lewis, The Four Loves
"There's room in our line of work for hope, too." Stephanie Brown
Stephanie Brown Wiki, My Batman Universe Reviews, Stephanie Brown Discord
No, I'm really with you on this one, and I'm actually liking the storyline pretty well so far. Like...they should have told Roge Antonio, "WE'RE GOING WITH BARROWS HERE - STEPH TOOK OFF HER MASK FOR REASONS."
(I really like this random all caps script for my comic creator's fake conversations for some reason.)
It's not hard at all! For Birds of Prey, I just defend the awesome muscles Claire Roe drew, and the fact that they actually do continuity with pre-flashpoint and love to include lots of characters, and for Batman and Robin Eternal, I just defend all the stuff that Ed Brisson didn't write. Haha. That's unfair. There are so many specific issues and moments I love about BRE, which I think are unfairly undervalued. Does it have serious problems and a really dumb ending with Mother turning into a ninja for no reason? Absolutely. But #13, and Cass in general, and Steph sassing Scarecrow, and Tim saving the day at Spyral, and Damian telling the Robins about his father's vision for Robin - those and so many more are gold.
"We're the same thing, you and I. We're both lies that eventually became the truth." Lara Notsil, Star Wars: X-Wing: Solo Command, Aaron Allston
"All that is not eternal is eternally out of date." C. S. Lewis, The Four Loves
"There's room in our line of work for hope, too." Stephanie Brown
Stephanie Brown Wiki, My Batman Universe Reviews, Stephanie Brown Discord