Which of the Following Categorizations Is Commonly Used Among Gerontologists

Which of the following categorizations is commonly used among gerontologists to classify the senior population?

A) retirement age (50 to 65) , old age (66 and over)
B) mid-age (50-64) , old age (65 and over)
C) young-old (45 to 54) , middle-old (55 to 64) , old-old (65 to 74) , and frail old (75 and over)
D) young-old (65 to 74) , middle-old (75 to 84) , old-old (85 to 89) , and frail old (90 and over)
E) least old (65 to 74) , average old (75 to 84) , old (85 to 89) , and very old (90 and over)