How old is middle age in numerology? (Be detailed)

Generally speaking, the ancients divided the time like this: when children were under 12 years old, and when they were over 12 years old, they were called the age of young generals. The weak crown at the age of 20 is youth. Some people think that after 18, a young man stands at the age of 30 and he enters middle age. His 50-year-old is called a mature fate, and of course he is old. 90 years old is 100 years old ... according to developmental psychology, it is divided into: lactation 0- 1 year old infant period 1-2 years old preschool 3-6, 7 years old preschool 6, 7- 165438+.