Ridley has made it pretty clear that Deckard was a different model than the other Replicants, which would explain his longer lifespan. He said people who don't get that Deckard is a Replicant are morons(his words, not mine).
I mean, Ridley has been involved with the development of this film from the start. There's no reason to think he would somehow go back on what he's been saying about Deckard being a replicant all this time. Also, the Replicants are not robots. They do age. I think some of the people you mentioned are simply suffering from a severe case of confirmation bias.