I'm also a Comcast customer, but I'm nearly certain I didn't get an IPv6 deployment until at least 2013/2014; I remember looking at their rather hidden signup form for beta testing IPv6 in ~2012, and I remember it being a rather long wait after that before it finally happened.
(Some places definitely were seeing initial rollouts around that time, but it was a far cry from "all".)
I guess they officially started rolling it out in 2012. I'm in Atlanta and I noticed my modem's IP mode flip to "IPv6 Only" sometime in 2011. I've been hosting from two different machines since then and about 30% of my network traffic is IPv6.
(Some places definitely were seeing initial rollouts around that time, but it was a far cry from "all".)