My French is not perfect, so it might be better if I'll write in English.
I'm not exactly sure if the source is correct. I took it from French Wikipedia (Dietrich von Choltitz). Wikipedia specifies the source as Dietrich von Choltitz, op. cit. (1969) pp. 204-206, but I can't seem to find this reference.
It's a known quote. First part of it (Je me trouvais devant lui et je vis un homme vieux, voûté, [...]) appeared in this German newspaper (Nun stand ich also vor ihm und sah einem alten [...]).
I think that this translation of Soldat unter Soldaten's title is official. I just made a typo (les instead of des).