While I've never drawn any age progression for my characters, Zei comes the closest due to the fact I've been drawing him for the past 8 years. I've done one drawing of him as a kid, and one of him as an Eggboss, where he's gotten older.

But apart from that, the way I handle things is each redesign of him keeps 3 things from his original design; his orange glove, his red and blue sashes across his chest, and his inhibitor rings. Because of this, I treat each of his iterative designs as his age progression in a sense as he originally started out as 12, and now in his current design is 21. He ages with each redesign, so in a sense the way his appearance changed if I try to put them together cohesively is:
-He started out short, full short, brown fur and brown eyes
-His fur grew out a bit, and his tail picked up some grey colouring around the edges of it, and he adorned the first prosthetic that Gears had given him
-As he grew older, his tail became fluffier, his ears began to turn white from the tip, black highlights formed round his eyes and he picked up a scar on his snout, as well as one on his upper left arm
-He gained a new prosthetic that was more jagged looking, and he began to wear the first version of his current outfit
-He gained a lot of height as he went past his 18th, his hair grew out further into a mullet, his current prosthetic was given, he lost the scar on his arm, and the white tips of his ears turned into white stripes, and his snout grew longer somewhat
-Now, the white stripes on his ears went back to white tips, and the stripes a dulled brown. The black markings around his eyes now turned into a full face pattern of the same brown, he shaved the sides of his head but kept the long fringe, which is now swept up and back, and kept his mullet. The grey on his tail now turned into white tips with some brown striping, his lower legs picked up white colouring, he now naturally stands on his toes due to how he traverses the world, and he's picked up a somewhat curled down upper lip, as well as his eyes going from a dark brown to a bright orange
-As he grows older, via the Eggboss design, he gets his other arm replaced with another prosthesis, as well as his right eye. His hair begins to grey. He lets a somewhat short beard grow out, and has picked up some noticeable fatigue marks under his eyes due to age and stress from his mental condition.

There's plenty more to how his character has changed as he's "grown up", but the rest of that ties more in to his attire, mental state, life goals and personality as he's gone through a metric fuck ton of changes