Pity you just missed
NaNoWriMo. No, don't wait until the next one to get started.
I don't know what your block is, and it sounds like maybe you don't either. I'm
guessing that you have implementation anxiety, but maybe not.
Either way, my suggestion is to sit down for X minutes a day and
write. It really doesn't matter if, while you're writing, you think "this is absolute rubbish!". It really doesn't matter if it doesn't quite make sense. That's
great! Once you have
something written down, you can push the words around until you're happy with them. Absolute rubbish is a thousand-fold more useful than a blank page.
Write page #16. Then page #17. Once you've got
all the pages down, then go back and edit. You'll probably have to change whole chunks but that's fine. For now, you're just providing the raw written material needed for that process.