At his old age, I think his ratio is 1 or two seasons and there won't be more than that.
You're wrong. Harry Kane still has like five years of top level football to offer. 3-4 at the very least.
Kane is among the top three best strikers in the world right now. If he wasn't worth that long the Bayern won't be offering that much to sign him. He will be a perfect fit for Bayern, but an Englishman in Bayern Munich is what I doubt will happen.
It might even be easier for Bayern to get him than the other premier league teams that might be interested. Tottenham wouldn't like to sell Kane to a club in the premier league. They don't want to give him to a team that would play against them.
Tottenham will actually yeild a little bit because if they don't sell Kane this season they'll definitely lose him for free next season because Kane doesn't look like someone that is ready to sign another contract.