There has got to be a reasonable statute of limitations. For example, Italy should not be expected to pay for excesses committed by the Roman Empire.
But what should the statute of limitations be? It's a judgment call, but there are still Greeks alive today who suffered under the Nazis. And their children are worse off because of it. So I'd argue that in this case the statute of limitations has not run out.
Of course, any money Germany gives to Greece would just be wasted. And it would start a cascade, where have-not nations would make all sorts of claims against the have nations.
My dad lost his house to the Japanese in WWII. He was a kid living in the European Community in China. Never got it back. Spent 3 years of his life in Japanese concentration camp a la Empire of the Sun (movie). He and his parents never were compensated one cent. Came over to the US penniless. When I asked my uncle about filing a claim for compensation, he indicated that Belgium (they were Belgian nationals) had agreed as part of the peace to waive all claims.