Yoga Vasishta on Human Life Span
In Book 3, Chapter 54 of Yoga Vasishta, Goddess Saraswati, the deity of Wisdom and knowledge talks about human life span:
Saraswati: According to the order that existed in the first creation, human beings were endowed with life span of one, two, three, four hundred years. The shortening or the lengthening of the life span is dependent upon the purity or impurity of the following factors:
- Country/ Planet/ Place
- Time/ Yuga
- Activity of people
- Materials used and consumed
Other texts fix human life span with the Yugas.
There are said to be four Yugas, the human life span in each respective yuga is said to be as belows:
- Kali Yuga (Length of Yuga:1200 years): 100Â or 120 depending on the text
- Dwapara Yuga (2400 years): 200/240 years
- Treta Yuga  (3600 years): 300/360 years
- Satya Yuga (4800 years): 400/480 years
These two fit very nicely. Since In different Yugas people will have different level of consciousness there will be difference in the quality of activities they do, and the materials they consume.
In a higher age people are very conscious, they do not adulterate food, they work as if it is service, they eat & drink healthy foods over tasty ones, they live with peace and equanimity and thus longer life spans according to the scriptures.