Possible Clues:

• Adolescents
• Youngsters eat greens for development
• Young people
• Young people unhappily eat greens
• They're aged between 13 and 19
• Much of the audience for 6-Down's show on 2/9/64
• Those growing up eat greens with difficulty
• Lots of new drivers
• One side of the generation gap, often
• Perhaps it led a nineteen