man vs. boy

How do you explain the difference between a man vs. a boy to a 2-year old? McKenna calls every male a 'boy'. It doesn't matter if they are 3 or 83. Sometimes it's a little embarassing. This evening she was watching our neighbor (who is 70+) through the window and asked, "What is that boy doing?" We tried to explain to her that he's a man. "Huh?" We continued by explaining to her that adults are men and that kids are boys. She sat there for a moment before she finally said, "But, I'm not a boy." OK, she's clearly one up on us. We'll tackle that one another day.