I think there are 2 different types of people who bike tour:

Type 1's primary love is the physical process of riding their bike. Going on a tour is a way for them to ride their bike a lot. As an aside, they also get to see some nice scenery, etc.

Type 2's like to mosey along, enjoying being outside and taking in the sights, meeting new people, etc. Traveling by bicycle gives them a good way to engage in that activity, plus they get some exercise. They like riding their bike, but that is not the primary motivation for why they are out there.

I'm not saying one approach is better than the other, just that the two types approach touring much differently. If you're a Type 1, riding 100 miles per day isn't that big of a deal. In fact, it can be a challenge. For a Type 2, riding 100 miles every day would be mental torture, even if they were up to it physically. Not fun. Similarly, limiting your riding to 50 miles per day for the Type 1 would drive them crazy. Type 1's and 2's can both enjoy the same tour, but they don't do well riding together (been there).

The point is, if the OP is a Type 1 and if he spends some time on his bike getting ready for the trip, 100 miles per day shouldn't be that tough. If he's a Type 2, it won't be any fun even if he is in shape.

I think having these 2 different types makes it more difficult to give and receive advice on this forum, since it's hard to know where the other person is coming from.