I have written a 150 page story about a 14yr old girl in 1969 it is in diary form and is actually titled Fourteen in Sixty Nine. My problem is what age group would I aim it at? Kids today wouldn't understand half of the terminology or identify with music, fashion etc but the older end would. But because it's about a 14yr old would it be right to aim it at maybe 50 plus age group who would have more understanding? Not sure what to do.
I think it also depend on what themes or issues you have the protagonist tackling and what age they are at the end of the book.
Tom Sawyer was written for children. Huckleberry Finn was written for adults. Both books are still being read - and loved - by all ages. I must admit that I've only read Sawyer about 4 times, while I've read Finn well over a dozen.
And Carroll's 2 Alice books remain in my top 3 books of all time.
If you remember neither The Secret Garden nor The Catcher in the Rye were written for children or 'teens', although they seem to be designated in those categories now. The age of the main character shouldn't dictate the audience for the story.
Depends on the slant of the story, do you know a 14 year old who would read it and give you some feedback? Or why not post it up in shared work, it's difficult to give an opinion without reading the work?