In my experience, there are 2 variables that need to be experienced: daily distance and weight.

If you plan to ride 50+ miles a day, you have to know that you can do that day after day. Even a fit 24 year old (and your partners) can be sore or have bike riding mechanics that make that kind of riding hard, even painful. Also, you will get more fit as you ride, so instead of putting the hard days first, try to plan a few easy days at the very beginning of the tour to acclimate you to the experience.

It is also very important that you take a long ride carrying the weight you plan to tour with. Riding a racing bicycle 20 miles a day is a far cry from pushing a loaded touring bike 50 miles a day. It is easy to pack too much weight and to struggle as a result. At the very least, you must take a shakedown ride with your touring gear at a day's mileage just to see what that is like. Not only is good to test your legs, it might also convince you to select lighter gear or leave some stuff home altogether.

For me, I ride a bike for exercise 2 - 4 times a week between 15 - 35 miles. When I have a tour coming up, I slowly ramp up my riding and distance so that I am riding 3-5 times a week between 35 - 50 miles. I also slowly add weight to the bike until I can ride 2 consecutive days at my touring distance (50 miles/day for me) carrying all the gear I will tour with. Even then, the first couple of days I try to plan easier days just to ease into the touring regimen.

Being young and fit will help in your ability to do this tour. But, it is no substitute for proper training and preparation.