The “Hitler Youth” were formed *after* the Nazis took power, not before or during their rise to power.
The old guy is too old to be remembering WWI, which was only about 10 years before the events of Cabaret, with disgust and cynicism for the German Nationalist sentiment of the song. Perhaps he is supposed to be thinking back to the German Romantic Movement in the 1880’s. He would have been young then, and would remember the idealism of that time, and how it led to the German Imperialism of the 1890’s and early 1900’s.
How can he be too old?
The Hitler Youth was the youth organisation of the Nazi Party in Germany. Its origins dated back to 1922 and it received the name Hitler-Jugend, Bund deutscher Arbeiterjugend (”Hitler Youth, League of German Worker Youth”) in July 1926. From 1933 until 1945, it was the sole official youth organisation in Germany
- Wikipedia
As for that old guy remembering . . . maybe he was seeing into the future and smelling a Hogg!