David Ortiz and Nelson Cruz defied the odds and were productive until they were 40. They are unicorns, though. Even surefire Hall of Famers like Pujols and Miggy Cabrera were shells of their former selves for several years at that point.
The truth is that MLB teams (and other sports too) have figured this out, and stopped paying guys big money that late into their career, with only a couple of recent exceptions.
Vladdy's obviously determined to test free agency, which is his right. Like the Yankees did with Aaron Judge, let him see what's out there and prepare to match at the end. If the Mets end up going as high as $585, you can still pay that much if you want/have to, but if other offers top out at $450 or $500 million, you obviously match or beat the offer and bring him back.