Don't get discouraged! I only started training for a century the last week in January and I'm already up to 65 miles. Since everything I've read says you only need to have done 70 miles or so as a long ride before a century, I'm practically done with the necessary training.

The second day of those MS rides is the tricky part, so you definitely need to train two days in a row, doing half of the first day's mileage on the second day, and maybe training at a bit slower of an increase each week than I've been. I think I've seen training schedules included as part of the MS event literature, so you might check those out.

I haven't done anything like what you're trying to do, but I'd say you can definitely start working toward it. Just listen to your body and if you don't make it, there are always other achievements you can make instead like Muirenn says.

Also, you didn't really say if you are pretty new to cycling or not (just road biking). What's the longest distance you've done in a day to date?