Not entirely, if you remember Dunharrow and the Palantir. And then his other transformations, in Rivendell, in Lorien, in Rohan, and after the coronation, and more. Other than those, where would a 70 years old man grow?

In the films he’s much more unsure about himself and over the course of the trilogy you see him kind of grow into being the king so that by the time he takes the crown it feels like you saw the internal journey that got him there.

Well, in the books it was a 50 years long journey.

In the books of course we know that this period is what, like, a couple years of his very long life so that would feel more out of place.

Yes, I think we understand each other.

those kinds of changes bothered me as a teenager,

For me personally they felt strange because, ahem, Aragorn seemed simply unfit for his role. A person which wouldn't end up on that track.