An effect for the editing of the users phonetics would be a great addition.
A really good reference for that is the programm "PRAAT", which is developed open source under GNU GPL.
It works its magic only by algorithmic logic and without any AI/ML, thanks to the brilliant work of dutch Phonetics Scientists at the Amsterdam University.
In regard to "changing the age of a speakers voice" it works way better than any other voicechanger I have ever used.
(This program has a big influence on the software products made by Antares, I would presume.)
The official website for reference:
(Despite its looks, the program is still actively maintained!)
This would be an awesome feature to have as (near-)Real-Time, either as an effect in Voicelab, or maybe even as built-in voicechanger.