the years from birth to eight
Kinderhook
From birth up to five years.
The formative years of childhood play a crucial role in shaping a person's personality and development.
In their formative years, young people don't always know which direction to take with their education.
Neither. It would be "formative years."
Claes Oldenburg The Formative Years - 1975 was released on: USA: 1975 (San Francisco International Film Festival)
Adolescence
Pythagoras was born in the country of Samos, but spent most of his formative years in Egypt.
In his formative years he attended Michigan School for the Blind in Lansing Michigan.
The mintage figures will not be released until 2010
Because those are the years in which a child develops their personalities. Psychologists agree that by age 5 or 6, a child's personality is set. When they are viewing and understanding the world in their own unique individual way, they are in their formative years. After these years, they are now set for who they will be the rest of their lives (generally).