How old is too old to read fantasy books?

So I'm 31 and I was talking to a friend about FW and IF and she laughed and said I should stop reading such childish books and I'm too old for fantasy. Most of the characters of the book are in their early 20s though which isn't exactly YA.

I get that people do think of fantasy as more of a YA genre but it really got me thinking about whether there are other people my age here?

Edit: I read all genres but hadn't explored much of fantasy until now. Clearly, that's about to change! And this topic came up because she said reading isn't really a hobby because you don't do it for fun, you do it to learn. And now that I'm typing this it's sinking in just how ridiculous our conversation was.