I'm norwegian and this pretty much sums up my experience. I have never studied english grammar and didn't really start reading a lot of it until I was around 16. From then on I mostly read english. I haven't really tested my english formally apart from getting As and Bs in High School but I think it's good, my reading comprehension is great. I dont think any intellectually curious (and young?) person needs anything more than an electronic dictionary and an access to the internet to learn it. The question is; can I do the same with chinese and spanish at 20?