When proper nouns describe a period in life, they frequently take the definite article:
"...what the young Einstein brought to the scientific facts was..."
"The Napoleon after Waterloo was nevermore the Napoleon of Austerlitz."
"The Africa of old doesn't exist anymore."
Sometimes, however, such nouns don't take articles:
"What kinds of things did colonial children, like young George Washington, do for fun?"
"... few delve into the personality of young Washington during his first experiences as a military leader."
"Yet young Einstein also made contributions to early quantum theory of such importance — ..." etc.
What is the difference between these two usages? How can one tell when not to use "the" with such proper nouns?