How is the lifespan of a human divided ?

Age is measured by years in life and every birthday is a sign of the age attained by a person and the years gone by since birth. One of the most important points telling on a person age is their years of life other than the visible manifestation of age, say for example, wrinkles and white hair.
Lifespan of a human being is divided in the following ways:

• Infancy – starts from birth till the age of 2
• Childhood – starts at the age of 2 and lasts till 12 years
• Adolescence – starts at the age of 13 and lasts till 20 years
• Early Adulthood – starts at the age of 21 and lasts till 34 years
• Middle Adulthood – starts at the age of 35 and lasts till 54 years
• Late Adulthood – starts at 55 years and till end of life

Human lifespan can also be divided by decades. Here is alook at how this is done:

• Denarian – between 10 and 19 years
• Vicenarian – between 20 and 29 years
• Tricenarian – between 30 and 39 years
• Quadragenarian – between 40 and 49 years
• Quinquagenarian – between 50 and 59 years
• Sexagenarian – between 60 and 69 years
• Septuagenarian – between 70 and 79 years
• Octogenarian – between 80 and 89 years
• Nonagenarian – between 90 and 99 years
• Centenarian – between 100 and 109 years

Human being remains the most active in the period starting from infancy to middle adulthood. As late adulthood sets in, they see the signs of aging and their ability to function is not the same because it changes or reduces. Each period of human lifespan is marked by changes in physical characteristics. The ripest ages range from adolescence to middle adulthood. With late adulthood, youthfulness disappears. People who are Sexagenarians, Septuagenarians, Octogenarian, Nonagenarian and Centenarian clearly show visible and internal signs of old age such as winkles, while hair, loss of movement and decrease in thinking capacity.