I do a somewhat hilly training loop, 5 k around, about 10 14 or 17 miles for training rides during the week, and am comfortably doing flatter stuff of 30 plus miles on the weekends... hoping for a metric century later this month.
It's going to be tough, but it's not a particularly tough century ride. It's the New York Century, which can't possibly have the kind of climbing that the tougher rides have.
Either that, or I'll just do the Montauk Century course (the 100 miler from Babylon Long Island) solo in September sometime. I have the cue sheets for it.