Considering the peculiar genetic projects of the Bene Gesserit and other Dune groups is unnecessary: the real world trend of somewhat aged people looking so good that they can pass as significantly younger (in particular, actors who are credible as younger characters) can be easily and obviously extrapolated to the wealthy nobility of a far future high tech SF setting.

Jessica Atreides at about 40 is supposed to look so extraordinarily youthful that a younger actress like Rebecca Ferguson is needed.