@Northern
Taiga is an average Japanese teenager. According to the current consensus, Adult Japanese males have an average height of 5'7.4. But we also know that Taiga is a 'shrimp' who is shorter than the average, since he's exactly the same model as the main character from Holyland. (I love that series. Maybe I should go read it for the 4th time)
Saying he's 5'5 would still put the mammoth between 20 and 24 feet high. Which seems too big, considering the largest one found was the 17 foot tall one I was using as a reference. https://scribol.com/science/paleontology/the-largest-elephant-that-ever-existed/4/
Admittedly, that's a skeleton. And the 'meat', fat, and fur on said bones could add quite a bit of overall height to the shoulder. Just not THAT much, lol.
I think that no matter how much 'realism' the artist usually tries for, we're going to have to just set this particular instance as 'artistic liscense'.