Thank you! I started less than a year ago, and I was the #13th biggest contributor here, and received a commit bit a few weeks ago. It's not too hard to get involved if you'd like!
I wrote up my own personal 'contributing to Rails' guide here: http://blog.steveklabnik.com/posts/2012-07-05-how-can-i-cont...
The official one is here: http://edgeguides.rubyonrails.org/contributing_to_ruby_on_ra...
The easiest way is to write documentation; that's how I got started. It's not for everyone, though. The simplest possible way to get involved with writing code is to pick an open bug on the tracker and fix it.
Like most things, it just gets easier the more you do it. The first one seems hard, everything seems confusing. But by the time you've done two or three, you wonder why you ever thought it was difficult.