I believe Eric had a passion for bodybuilding before getting into cycling. Once you put on enough muscle it's very difficult to get rid of it, but he's lost a ton of weight. I know bodybuilding has a tarnished image, just like cycling, but having once been into lifting weights I can say that you sure learn how to use your body well, and very symmetrically at that. Being able to have great control of all the muscles is a huge advantage in any sport.
He's very smart, focused and most importantly, consistent. I've seen his power files before and the w/kg are very good, but nothing to make me shake my head (~4w/kg for 4 hours indicates discipline, but is not insane). He fits the mold for domestic success, where most races typically don't have climbs more than 8 minutes and are 100-180K at most. High absolute power, especially for his height (aero advantage), combined with a respectable strength/weight power means that he's going to be very good when it comes to sprinting to the line from a breakaway.
It shouldn't come as a surprise to see guys who came to the sport later in life do well later in life too. They still have the fire that guys who've been doing it for 20 years can't sustain. It's very difficult to keep the passion more than 8-10 years (just ask your ex-wife!). Without the need to be elastic/resilient, as in running, cycling is very well suited for the seemingly-past-the-prime endurance athlete THAT IS STILL MOTIVATED to train their butts off. If the genetics are there waiting to be developed as a 15 year old, they are still there waiting as a 25 year old, so I don't see it mattering too much which age one starts at in regards to cycling so long as they are passionate about sport and athletic development of oneself consistently all along the way.
Obviously there are great age barriers that can be difficult to get past due to the rules of requiring a bunch of young guys on a Continental team, but if you can get yourself to enough of the big races every year on an elite amateur team you'll eventually realize your talent 5-8 years after getting started, just as any 15 year old does. Think of how much more discipline, financial and emotional consistency you had at 35 versus 25. As a 35 year old, given the same fire to train and compete, and with the same amount of time invested in the sport (say 10 years) the 25 year old version of myself with identical passion and time in the sport (10 years) would never stand a chance.
I reckon a LOT more 30 something year olds would be winning if people didn't wrap their lives into a big drama (car, wife, kids, house) straight out of high school and not be able to financially support "living the dream" beyond the age of 21.
Congrats to Eric, he's really a stand-up guy.