Do you have a specific book in mind? 
The book we’re about to start, Home Thread for 소리를 보는 소년 👁👂 Korean Fiction Book Club 🇰🇷 Starting Nov 13, is probably around the early 20s I’d say (it has a temporary rating because it hasn’t been graded yet). I’m reading a bit ahead so I can fill out the reference sheet with vocabulary and grammar (link in thread), and there are others willing to help if you have questions. 
I wouldn’t mind reading along with something easier at the same time if you already have a book in mind, though. 
