The twelve planets describe different ages or stages in the human and divine life cycles which are two halves of the same unit.
Only seven of these, known as the Seven Ages of Man, are commonly dealt with in astrology, based on the traditional seven planets, and even here the role of the Sun is not properly understood.
The Seven Ages of Man, which are also the seven ages of creation and other universal cycles are as follows...
The Sun: Your divine, godly, or pre-incarnational self
The Moon: infancy or the first four years of your physical life
Mercury: childhood or the pre-teen years
Venus: teen life or adolescence
Mars: adulthood or the prime of life(some mistakenly put the Sun or Earth here)
Jupiter: middle age or the productive years
Saturn: old age, senility, and death
What about Uranus, Neptune, Pluto, Earth, and Vulcan? Surely these must represent important stages as well? They do.
While the planets from Moon to Saturn represent human or earthly life, The Sun and the other five, with their much longer orbits, represent divine or heavenly life.
Uranus begins the road to divinity or immortality by breaking the material concepts or limitations of Saturn and freeing one's mind or spirit to the truth that leads to eternal life. Christ, Buddha, Krishna, and other avatars were Uranian in that they showed us the way(truth) to transcend the apparent limitations(deceptions) set by Saturn/Satan.
Neptune continues the process by infusing us with the full measure of the Holy Ghost, Spirit, Prana, Chi, Universal Life Force, etc. which opens up the higher psychic senses and gives us a collective or bird's eye view of life and reality -and enables us to see where we are going or must go.
Pluto dispells all uncertainty or illusion and the choice becomes clear -regenerate or degenerate. Parts of you die and others are refined or rebirthed, leaving only that which is good or essential.
The next two planets, which are to be officially recognized as such by astrologers(Earth?, Vulcan?) or X and Y, represent the ensuing stages of judgement, balance, mastery, dedication, purity, perfection, and service.
Finally there is the Sun itself which is the outward, visible, or manifested symbol of divinity and/or godhood. The Sun's true orbit is the longest of any of the planets measuring in the thousands of years around an as yet undetermined greater star or god.
In summary, there are six earthly or human stages represented by six planets(Moon to Saturn), and six heavenly or divine stages represented by another six planets(Uranus to Sun).