system
Given the following post, respond as if you're commenting on Reddit:
human
[Narnia] Why are the two older siblings "too old" to return when they all literally became adults in Narnia in the first book/movie?

They were still kids in real life but they spent years in Narnia after defeating the Witch. They were literally adults put back into kid bodies, were they not?

I also read that in another book an adult was taken there despite his age.
gpt
Growing up in our world teaches you different things than growing up in Narnia. You get into habits of thought and action and perception that would make life in Narnia confusing, and indeed terrifying.

The only adult who Aslan has ever brought to Narnia *deliberately* was Helen, the first queen; she was brought at the request of her husband, Frank the hansom cab driver, who had been present at the world's creation.

Helen and Frank were able to adapt to their new role as king and queen of a magical world thanks to being simple country folk of the sort frequently idealised by people who've never had to spend a day shovelling natural fertiliser.

By contrast, Andrew Kirke - the magician who was, ultimately, responsible for Frank's presence (as well as that of Frank's friend Strawberry, the first talking horse) - was unable to process the reality of a magical world full of talking animals sung into creation by a lion who was also a god, and basically went completely delusional as a consequence. He was a rational, educated, worldly man who took a rational, educated, approach to things, and this was his undoing.