Every human being, regardless of their horoscope, goes through the same sequence of natural development. These natural eras in human life (“naisargika dasha”) are the same for everyone:
Birth – 1 year: The Moon
1 – 3 years: Mars
3 – 12 years: Mercury
12 – 32 years: Venus
32 – 50 years: Jupiter
50 – 70 years: Sun
70 – 120 years: Saturn
When humans are born, the first thing we do is rapidly build the power of concentration and awareness in our minds. Thus the first year of human life is governed by the Moon.
The next thing that happens is that our bodies grow fantastically and we develop muscular strength. Thus the ages of 1 – 3 are under the governance of Mars.
With our mind and body now ready to function normally we are ready to begin speaking, interacting and learning. This period of primary education begins from the ages of 3 – 12, under the governance of Mercury.
Having primary knowledge under our belts, we move into the next phase of life: vocational and higher education and the building of our own lives by getting married and raising a family of our own. These years 13 – 32 are governed by Venus.
Having accomplished all our education and the bulk of our practical responsibilities we now attain a period characterized by wisdom, prosperity and the ability to guide others. These are the years 33 – 50, governed by Jupiter.
Wisdom and guidance leads to recognition, leadership and fame, which come during the Suns natural period of life: the years 50 – 70.
Finally we detach ourselves from material things and prepare to understand the limitations of life and death. This occurs during Saturn’s natural cycle, the years 70 – 120.
These are non-personal eras of life, in that they apply to everyone equally regardless of who they are. It is said that when an individual has a personal era (“dasha”) in coincidence with a natural era of life, the planet concerned becomes extra effective in a positive way. I have personally experienced this to be a valid logic, making it a fit topic for further consideration.

If you are reading a chart, there are three considerations to make for each planet: