I'm putting together a chart but just so you get an idea, them in order from tallest to shortest goes: Dagger, Thorn, Arid, and Gobi
Also ages are never specified because there isn't a specific year this story is set in.

But if I took the entire story timeline and chose their ages right in the middle of it:
Dagger's avg. age is 20
Depends on the month...but Thorn would also be 20
Then Arid would be 18
Gobi would be 10

It's kinda complicated-