I have done a few quad centuries (a century a day for 4 days). It isn't a whole lot worse than doing a century. The important thing to do is watch your pacing. If you push too hard, you will pay for it. If you are beaten up on the first day and are more beaten up on the second day, well the third day will not be fun.

I always found eating quite a few carbs is important. You will need to replace your muscle glycogen which will almost certainly be nearly exhausted on each and every day.

As for training, try to get in a good aerobic base as soon as you can. The more aerobic base you have, the better. Once, you can ride in your area, try to ride routinely as many days per week as you can. Try to do some long rides like 70 miles. Also try to do 70 miles or more back to back. That sort of thing.

But do what you can. Any training you do is better than the best training that you don't do.

Good luck to you

Pat