Emo,
I'm 18. I've had the same concept for years - probably since I was 14 or so - and just started writing the WIP this summer. I finally realized what took me so long to get the thing on a page, and that's because at 18, I'm vastly different from the person I was at 14. I'm more educated, I've sat through all sorts of classes on history, philosophy, language, sociology... etc., the list goes on. I've taken all sorts of bits and pieces from these classes and real life and put them into this story.
My WIP would not be the same if I had written it 4 years ago instead of now. Heck, even a week ago when I was sitting in class I got a new idea from a lecture by one of my professors.
So, anyway, while I'm certainly not saying writing now is something you can't do, just keep in mind of the changes that might occur throughout the years. Since you're on your second novel, then you already know you can write; you should just determine the right timing.
And as for writer's block... I have a couple of my favorite books I'll pull out and read my favorite chapters/sections... brief through a writing book (King's)... and simply sit in front of my computer and force myself to do something. It usually works out in the end...
Good luck!