First tour was a 3 day at age 13 with some friends.

We rode from the center of town about 12 miles out to one of the guy's uncle's farm. Spent the night, then rode to a campground near a lake, then home on the third day. Total mileage was probably around 35 or so. Not bad considering most of us were on single speed coaster brake bikes. IIRC one guy had a fancy shmancy "English Racer" 3 speed.
Next really serious tour I did was about 3-4 years later, 14 days on the Blue Ridge Parkway and the Shenandoah Skyline Drive. Biggest problem was food and not having enough cool/cold weather gear. Food was only available if you drove off the parkways, quite often 10 miles or more. That bike was a 15 speed that was built up on an old Motobecane frame set.
The bikes have gotten better over the years, the engine has gotten smarter...and slower.
Here is an
interesting story about a first tour, just shows what can be done.
Aaron