Some ideas take a long time. There are novels out there that authors famously have claimed “took ten years to write.” Like The Lord of the Rings and Gone with the Wind, sometimes that time can be allotted to some of the page count, but that’s definitely not the case across the board. For instance, Junot Díaz is said to have spent about ten years on The Brief Wondrous Life of Oscar Wao. J.D. Salinger spent ten years on The Catcher in the Rye which isn’t all that long of a book either. It’s not just about the page count but the idea.
I won’t say that no novel should take more than a year or two, because some just don’t. I’ve heard writers argue both sides of this. There isn’t a right answer. If you’ve been stuck and sitting on drafts, it may be time to stick them in a drawer and come back in a month or even seek out opinions from friends who write. Sometimes while drafting, if you decide you want to make a big change, you might want to think it through before going for it. What will this big change accomplish? Different is not always better.
Writing and rewriting a novel again and again with new drafts and revisions can be frustrating, but it’s exactly what every writer ends up doing before coming out with something polished. It’s a process and sometimes it can be really difficult. There isn’t always a right or wrong choice. Getting opinions and even seeking out an editor to give you editorial guidance.
Sometimes distance is also needed to pull off a novel. Most writers recommend putting your draft in a drawer for a month and coming back to it with a red pen. Read critically and dare to make realistic changes. If a change is too big, it’s becomes less of a change and more of a completely different book. Let the draft tell you what it’s trying to do, instead of the other way around.