Earlier quoted context omitted.
In a war of attrition (actually any war or even battle for that matter) the war is generally won by the enemy's morale breaking, not by literally running out of soldiers. When one side is losing and they know they're losing (or they see the conflict as not worth dying for), most people would prefer to save their own lives rather than die for nothing. So you get desertion, refusal to enlist, rapid surrender, and so on…
Many factors contributed to Germany losing WWII, but one of them was because they ran out of soldiers. They were down to using boys and old men.
So yeah as morale collapses you're left expanding the age of conscription, which further collapses morale. There were plenty of sardonic jokes about the Volkssturm, 'the people's brigade.' Why is the Volkssturm the state's most valuable resource? Because they have silver in their hair, gold in their teeth, and lead in their bones.
[1] - https://en.wikipedia.org/wiki/Befehlsnotstand#Nazi_Germany