Scary thought.
But if you can think, you do it. Right?

It must be possible to stop learning.
What would that situation look like? Meaning, am I living in that? Or could what I live in now be improved?
A coma would work I supposed. No dreaming. Dreaming might allow thinking which leads to learning.
Otherwise... Would you just have to be genetically made up not to learn?
I'm also thinking of a dull, tedious job.
Or having so much work to do that you never do anything new.

Or not having an interest in learning. If you're rich enough and people do everything for you and can just enjoy, you might just enjoy life without learning anything new.
Fatigue could halt or at least slow learning.
I suppose a brain chemical thing. If you mind physical can't produce new memories, new learning.
I'm still trying to stick with reality though.
Being in an isolated enironment, away from people, without materials. Without internet. Imagine that.
What else?
Because if you know how to slow or stop learning, you would also have a good idea about how to speed it up.