Daylia, you are assuming first:

That there is such a thing as a "true experience with God."

And second, that every perception of an experience with God would necessarily be "true."

Neither condition is something that one person can judge for another. If one genuinely believes that their heartburn is God talking to them, they are as unlikely to accept your dismissal as you are to accept their divine revelation.

"But you will agree, I hope, that actually having sex (for example) gives one more knowledge of it than being told the facts of life by your mom or dad when you're 14 years old or reading a book about it?"

I would say it merely gives you an experience; maybe bad, maybe good, maybe mediocre. In and of itself, it is not knowledge since every experience can be different and even the same experience can be viewed differently within one's own mental framework. If one says, "sex is boring,' does that mean they KNOW sex is boring, or does that mean their EXPERIENCE of sex is boring? Because you or I or someone else may have an entirely different viewpoint based on our own interpretation.

I would define knowledge as the collection of reproducable experiences of the self and others. When you add the individual viewpoints together, you can start to form a framework that can be accepted as knowledge.