The number 70 can be read as a two digit number but it is usually read as 7 and 7+0=7. The number 7 is defined in Chinese numerology as indicating ascension. It indicates ascension (7) to completion (8), and the ascension of the spirit. Confucius said that one can only achieve maturity of thought at age 70. Before that age, one needs to learn and study. Only after reaching the age of 70 can one think freely without having incorrect thoughts. Age 70 was regarded as old age in Confucianism. Of course, a 70-year-old grandpa may seem stubborn to the offspring at times.
The concept of the number 7 indicating ascension is also rooted in the traditional Taoist practice of “parking the coffin of a deceased ancestor at home for “qi qi si shi jiu tian” or 7×7=49 days before interment. This is still practiced by some wealthy families on Taiwan.
The number 70 is a very good number. In traditional Chinese folk belief, a family with a 70-year-old grandpa and/or a 70-year-old grandma can be a three-generation family (san dai tong tang, literally meaning three generations in one living room). A three-generation family is a prosperous family and a family of good fortune. In books and in folk tales, a three-generation family is praised.