Is there a difference between "20's" and "20s" (in either ages or dates)?
Such as, "he was in his mid- to late-20's" versus "he was in his mid- to late-20s."
Or, "the 1990's saw a surge of economic growth" versus "the 1990s saw a surge of economic growth."
M'aidez! (Or as the Americans would say: "Mayday!")