Is it possible? Yes, if you're comfortable on your bike for long periods of time, and your legs can hold out, it IS possible. If you plan on riding in an organized supported century, most have cutoff times, so I think you'd have to pick up the pace some.
How much time do you have to train for it? Do you feel like you're maxed out on speed, or think you can become faster? Again, it's all about what your goal is, and how good you feel on the bike. You probably wont be breaking any speed records, but anyone can ride any distance on a bike that fits them with the proper training.