I was commuting 30miles RT for about 6 months when I did my first century at the Tour De Palm Springs. No other training besides that. I had ridden 40miles in a day max up until that point which involved going someplace on way home from work. I found I didn't need more physical training but needed to tune my fit for that much time in saddle and work on my pacing. The first 50 miles were fun and fast. Last 50 sucked, but I did it. My commute I don't need to worry about managing nutrition or hydration most of the time or pace myself as I'll have 9+ hours of recovery between segments.