Thanks for the input Jo Zebedee. I was having a feeling it might be too good to be true when people were saying I didn't need to pin down the age range.
Of course, that still leaves me with the problem of what age range best fits? Is it harder to publish an overly long and older MC middle grade, or a non-edgy YA with a still wrong aged MC, or an adult fantasy but with a tone more associated with children's books? (The question is rhetorical btw, since I know it's too hard to answer without actually reading the material!)
What you said in your first post makes sense, at any rate. I was always worried I'd work myself into a corner and end up with a product that doesn't quite fit anywhere. But in the end, if I feel it's important to keep the general length/tone/MC age that I have, I can still try to do my best with it, just being aware it might hurt my chances at getting published. It is my first book, so even if the age range was clear cut, I might not be able to get it published any way! And self publishing is a consideration.
Lots to think about, at any rate. I'm hoping I can cut down on the word count a bit with this next edit, which might help clear things up!