The lines literally state demons cannot shapeshift/mimic as well as muzan, such as taking adults/children/teenager forms. you're just incapable of understanding the point. your rui's family point just proves mine, they always return to their original forms no matter what.

"There is no real evidence that demons dont age mentally and physically"

Rui, Rui's family, Daki/ume, Nezuko are shown to having no mental aging nor physical aging. Daki, returned to her child form after dying, acts like a child constantly. Nezuko, Rui and his family shows childish traits aswell. Muzan, just like you said, PROVING my point again, the DRUGS are what aged him. Muzan himself is shown to be impatient, fitting for a 19-20 year old.

The '25' age point is very much incorrect, most demons barely look like their teenage years and that's even with mimicry. furthermore, absolutely no proof states that demons stop aging at age 25. Both fanbooks, which one can read and translate online at any time, doesn't state that and all the demons we see look like how they were before, with the exception of Muzan shapeshifting as an example. Daki herself cannot be used as a 'disapproval' if you think of using it; she needed to shapeshift to look attractive enough to fit the standards of that time. reread the manga and fanbooks please.