You are just taking the best examples out there and assumed Kane would last as long. But in fact not every top striker could maintain their top form until their mid 30s though, even with the help of modern sports science. If we look at recent decade you may find a long list of top striker who start to decline during their early 30s.
Ruud - decline at around 32-33
Rooney - decline sharply at around 31
RVP - decline sharply at age 31-32
Higuain - decline at around 32
Cavani - decline at around 32-34
Augero - decline at age 31-32
Grizemann - decline at around age 31
I think chance is, Kane would probably maintain his top form for another 2 years or so, and after that we will have to see if he could extend his form for another 2-3 years.