It could also imply that they drive them less. People without money for new cars also generally might want to spend less on gas, or, might need to forgo driving until they're able to afford repairs. Several of the brands at the bottom of the list in particular are brands I see driven by older folks: Buick, Lincoln, Cadillac, etc. In rural areas at least, this often means retirees without a commute who may only take the car out for church on Sunday.

Other theories: Kids tend to inherit older cars from their parents, and may but fewer miles on them. Older cars might get used more as "the beater for around town" if the household has a newer primary vehicle. There could also be some geographical distribution that's a part of the puzzle.

Right, but it does change how I’d expect the results to be attributed, with brand not being the relevant predictor.