Why can't niż be used in this instance?
It can, but you have to remember that it uses a different case. "od" (here: "ode") takes Genitive, "niż" takes Nominative. So: "Jesteś starszy niż ja?"
Only option was "starsze" which seems unlikely, since it would appear to be neuter?
There's no audio for starze on the app
On this comment page (newest Chromium browser on laptop running lubuntu 18.04.1) there's the blue Sound button but no audio. [11 Feb 2019 10:13 UTC]
The audio button doesn't play anything for me, but it does play for me in the Incubator. Weird, last cases of missing audio (after introducing the male voice) were missing in both places...