I'm not doubting your (or your sibling's) claims, but I find it extremely difficult to imagine any older person preferring a virtual keyboard to voice messages (provided they are properly introduced to the feature, of course). Maybe this preference stems from how simple telegram (the app we use) makes taking and hearing voice messages? Perhaps it really is a regional thing after all. We need more data.

From my anecdotal/regional experience, people over 60 prefer to use voice messages almost exclusively while younger people prefer to text.

Maybe someone at telegram or whatsapp can provide statistical data to shed more light on voice message usage.