brinked - 7:07 pm on Jun 21, 2012 (gmt 0)
I've seen the occasional site start ranking much faster than six months. It's usually something that catches media attention for some reason.
Oh of course you can rank a site faster than 6 months. Heck a site can rank as quickly as a week. But it still will be held back due to its lack of age. Once it starts establishing age, it will rank better and better as long as its content/links/exposure warrant it.
A site with at least 6 months of age will be much more stable in the rankings and its just much easier to rank. A newer site needs much more stronger signals to rank quickly.