Wow. That seems really odd to me. In the UK, we have graded exams that we take as we advance with our instruments. The grades start at 1, and go up to 8. It's common for people to be taking Grade 8 after about 8 or 9 years, depending on their age. If you start at a young age (for instance, I started when I was about 8 or 9), then you're usually about Grade 8 standard when you finish school, as long as you're a good musician and pretty dedicated (I've recently started the Grade 8 syllabus).
But, of course, that excepts people who are exceptionally talented - I have a friend who achieved a Grade 8 standard on Violin and Piano when he was about 11.
I'd find judging your musical ability by the amount of time you've played for to be pretty inaccurate - some of my friends have played for longer than me, and can't handle a basic rhythm/tune, and others have played for a few years, and are incredible. Are there no graded exams whatsoever for music in the USA?