Does the pot have a hole in the bottom?

Those white spots could be from too much fertilizer. If you don't fertilize, it could be also from water - too many minerals in it. Minerals/salts crystallize on leaves if too much for plant. I think it could happen also from very rich soil, but not absolutely sure. I bet you can just wipe them off. Not that is the solution - just a check. It they take long time to reappear, they are salt deposits.

Powdery mildew can start as white spots, but hey are usually blotchy and bit bigger, and do not appear on all leaves. They often turn darker color, and could be also fuzzy. Powdery mildew is fungal disease. It could also be wiped off, but reappears much faster.

Soil you are using seems to contain too much organic matter. It should be well draining, and pot needs drainage hole as socks asked about.

Oldest leaves will shrivel and dry up, but there shouldn't be too many at the same time. They could do that also if improper watering-drainage.

The pot does have a whole but the soil could very well be too rich. I can't remember what I used to re-pot it. I do occasionally fertilize it... so the mineral spots are a good guess. Thank you for your, rina_Ontario!