Having a big dick would help (seeing as how someone with eight inches has a three-inch advantage over someone with five inches when it comes to how far you have to bend), but the vast majority of the distance is covered by bending anyhow.
I wouldn’t say that anyone can get flexible enough (seeing as how different guys are naturally going to have different maximums to begin with) and any number of factors - including age, weight, fitness level, genetics, diet, time of day, and countless others - play into it.
But I would say that a lot of guys probably could reach (or at least get close) if they work on increasing their flexibility over time - just be sure to be careful so as to not hurt yourself from trying too hard, too soon.