[samatman]

This is the basic problem with adapting Dune. It has absolute loads of worldbuilding, and tells a reasonably complex plot at the same time. It doesn't matter how many times it's adapted, the viewer is just going to have a better time if they have read the book.

Jessica is a Bene Gesserit, they are explicitly noted to stay youthful in appearance and live a long time. This is one of many hundreds of details that just have to be shown, there's no time to explain them.