I don't know why people think players aside from the big 3 (+ Murray) will be playing at age 36. That is an extreme anomaly in tennis history, almost nobody in the history of the sport played professional tennis at 36.
Even more recent generations on players like Raonic, Berdych, Roddick, etc. all quit in their early 30's. A handful of players in the OE were actively on court at that age and capable of winning events: Laver, Rosewall, Connors, big 4, Feli, Isner and a couple others. Andre played only a few matches after turning 36. Stan and Gasquet are still active but couldn't win a 500 if their lives depended on it.
If Zverev is losing first and second round in every even when he's 29/30, he's not playing till age 36.