There is an audio voice manipulation plug-in whose name I do not remember with two basic knobs: more masculine ⟷ more feminine, and younger ⟷ older. So it is not merely a simple pitch shift that is going to do it, it also needs to be combined with a compatible formant shift and possibly further processing depending on the settings.
Comedian Felicia Michaels has the highest speaking voice I’ve ever heard. From Star Search, but still NSFW. Starsearch - YouTube