(Resubmitting, from memory, with some additions) How much time has passed since MOM/the start of the Omenpath Arc? I know wizards likes to keep it vague but Kellan looks like he’s aged 10 years (exaggerated) since he was first introduced in Wilds of Eldraine. Going by hair length, maybe 12-18 months?I've seen this comment a lot, but the simple answer is that Magali Villeneuve does glamor shots and tends to age up younger characters for them. See also: her art of the Kenriths when they were in their late teens. The actual timeframe is forthcoming but honestly, your hair length guess is pretty accurate, it has been over a year since MOM.
This key art show Kellan closer to the appropriate age range, but remember that depicting likenesses is tough to the point we're extremely lucky that Magic characters look like themselves so much over, in some cases, dozens of pieces of art.
toweringclam:
Thanks for the answer! I think it might be especially hard to get Kellan to look like himself since his whole thing is blending in (while still not quite fitting in)
There is the additional problem of not much reference material existing for him for artists, as pretty much every piece about him was likely commissioned in the same year and all variations on whatever concept art they had,