I'm assuming you're referring only to the main protagonist or narrator.
I think it depends on whether or not you are writing in first person. If you are, it's going to be a lot easier to do without having to say 'the boy in the ragged shirt' or 'the youth' every two sentences or so. If used correctly, it could add an element of mystery to the entire novel. However, you must make sure that the reader will not get too flustered trying to keep track of what's happening (the death knell of any book).
If you could do that in third person, I think it might help if you kept the cast of characters small, or, made them very different from the main character (a boy in a world of men). It would actually be a nice literary touch on your part, and it might even help build suspense.
(see the short story 'The First Miracle' by Jeffery Archer. I know, it's not a novel, but it's still a nice read).
Another story that keeps the identity of one of the pivotal characters a mystery, and indeed, only alludes to his true identity throughout the entire novel, would be 'Master and Margarita' by Mikhail Bulgakov. It's funny and witty, and definitely worth your time.
There is no hard and fast rule, really; it all comes down to your skill in the end. Write the story, set it aside for a week or so till you've forgotten about it, and then re-read it, pretending it's someone else's work. See then, if you get that magical desire of wanting to turn the page to find out what happened next.