I’ll start off by saying that imaginary friends do nothing for gaining experience.
An imaginary friend is something you can control, they are a part of your imagination.
It doesn’t help you with learning on how to sense or communicate or interact with spirits, and it certainly doesn’t help with discernment.
I’d also like to point out that many of the people who want to count having imaginary friends as kids go back and end up counting the time between them having an imaginary friend and where they’re at now as years of experience. It makes as much sense as me taking a science class in elementary school and suddenly calling myself an expert microbiologist!
The only thing that should count towards someone’s experience level is years of actual spirit work, and nothing less than that.