(5-9|0-5)
That doesn't really make sense... it's the same as 0-9. Your regex can be simplified to: /^(19|20)\d\d$/ Which doesn't meet the requirements.

If you really want to become a regex master, the first step to enlightenment is to read "Mastering Regular Expressions" by Jeffrey Friedl. The link is to the publishers site (O'Reilly) but you can get it just about anywhere. That book taught me everything I know about regular expressions.