65-89 years old is an elderly person; 90-99 years old is a long-lived person and over 100 years old is a centenarian. The main features of aging are: graying hair, loss of vision and hearing, dry skin, and decline of knee joints. 1. Graying of hair: With age, the secretion of melanin in the hair follicles gradually decreases, making the black and bright hair slowly turn gray. Especially at the temples and the top of the head is the most significant. 2. Vision and hearing loss: hearing and vision decline from the age of 40, vision loss is caused by lens sclerosis and ciliary muscle weakness, and its main symptoms are blurred vision and double vision. 3. Dry skin: When you get older, the collagen on your face is gradually lost, and your skin condition gets worse and worse, with dry and rough skin, loss of subcutaneous fat, thinner and thinner skin stratum corneum, more and deeper wrinkles on your face and age spots on your face and back of your hands. 4. Decline of knee joints: Calcium maintains the bones strong and healthy, after the age of 45, calcium is gradually lost, bone and joint wear and tear is serious, no timely supplementation of calcium and vitamin D, lack of exercise, etc. can increase the risk of osteoporosis and bone and joint diseases.