The Young Adult (YA) novel length or word count is 45,000 to 90,000 words. Hard fantasy and science fiction writers can get away with 100,000+ words, but it might be a gamble if you’re going the traditional publishing route.
Agents suggest sticking with the guidelines above. Publishing houses are running a business so they take into account printing costs, how much storage space your book will take up, and other boring, yet necessary, business investment considerations.
If your novel length is towards the high end, then make sure it’s had a good editing. As a not-yet-best-selling author, a poorly edited book with superfluous text will make your rookie-ness stand out. Translation. Your writing won’t be taken seriously.
Once you’re a best selling author, you might be able to get away with a little more. By then you’re writing will have greatly improved but will never be perfect.
The above information is a guide. If you decide to self-publish, then you have total control over every aspect of your “book baby.” Also, there are exceptions to the above in the traditional publishing world a la Stephenie Meyer’s breakout novel Twilight which is 130,000 words.
I prefer to be positive and choose to believe anything is possible if you’ve got a great story with even greater characters.
Check out this article by Mike Wells. Not being able to get a traditional publishing contract doesn’t have to be the end of your writing world. He’s had great success self-publishing entirely in eBook format, so printing costs and storage space is a non-issue and might be something you’d want to consider.
Many authors, whether traditionally or self-published, break all sorts of rules and have great success. If you believe in what you’ve written, then go with it!