I Drink Your Milkshake!

If the world were a fairer place, when you beat someone younger than you at tennis (or in a fistfight or armwrestling or any other one-on-one physical challenge) then you would swap ages with them . . . you'd suck up all their youthful energies and become instantly younger and they would assume the burden of your years and become instantly older (and we're talking about consenting adults here-- no chucking an infant out on the court and whacking balls at them).