I feel the expression "under the platform" is awkward

How about this instead? (I agree that the phrase "under the platform" is awkward and even misleading.)

On the platform, the 87-year-old professor spoke loudly with witty words, while seated in front of the platform along with many other teachers and students, his young wife, 33-year-old Wen Fan , listened quietly.

She's almost too young even for me and I'm only 49!

Thanks

I think a parallel construction would flow better.

On the platform, the 87-year-old professor spoke loudly with witty words while in the audience his young wife listened quietly.

just a small tweak ori..
But I like the word dais better
(Dais is any raised platform located either within or without a room or enclosure, often for dignified occupancy, as at the front of a lecture hall or sanctuary.)

From the dais, the prof spoke loudly and wittily
...while in the audience, his young wife...blah blah

That gets rid of the problem of placing the listeners.