You’re old, single, horny and financially solvent. Why would you not want a 20 year old live in maid / fucktoy? You have no fucks left to give what anyone thinks, the girl is okay with it, so why not enjoy your last years? Transactional relationships are common all around the world.
Personally I’d want a partner more than a 20something fuckservant as well, but I can definitely see the appeal for horny old dudes with too much money. That also somewhat ignorantly precludes the possibility that the young woman has more to offer than her body though, which I’d think is quite likely in reality.