I'm wondering... the 20s...do you still have plaster & lath walls? If so- that can cause incredible amounts of dust. Try to consider it a small price to pay for a 1920s house with TONS of character though. Pets are walking dust bunnies.

our house is 17(ish) & it stays clean for about 10 minutes- I've given up. as long as I don't have science projects growing anywhere and the kitchen & bathrooms are clean I try to close my eyes when I walk through the rest of the house until cleaning day.

Ok, so I'm OCD too.... swiffer dusters seem to keep the dust from coming back for a day.
3a/b mix