Welcome to the forums JunoJim
You’ve picked a very good brand of blank media. They should be as good as anything out there. That’s the good news.
Reading the disks shouldn’t degrade them. But all burned disks will eventually fail, the question is when. 100 yrs seems excessively optimistic to me. DVDs that are known to be good brands, burned and stored properly should last at least 5yrs, as a conservative (pessimistic) estimate, and will probably last twice that without issues. Until burned dvds have been around a lot longer than now, we won’t know the average lifespan of the disks. There are tests used to estimate lifespan, but who knows how well they relate to real-life situations.
Proper storage and handling will help keep them in reasonably good shape for a long time. Handle them by the edges, store them in a cool, dark place and don’t expose them to excessive sunlight. Many people advocate putting them in individual dvd cases for storage, and others like the hanging sleeve type of storage.
You should look through the FAQ in the Blank Media forum: http://club.cdfreaks.com/f33/media-faq-61943/ The second and third entries should be applicable to your questions.