The body changes all cells every 7 years. The physical changes yet something persists in man - the soul.
0 to 7 - physical body
7 to 14 - etheric body
14 to 21 - astral body
[This is the reason every significant life event has its place; for example: if you start your sex life very early you won't develop to your full potential, let alone the other shortcomings]
Cycles continue further with the individuation ("I") and the development of the sentient, intellectual and conscious soul.
Humanity has a similar development and each of the living have more or less to play by the rules of the game (current level). Eventually man will reach the spirit-man (for most of the remaining this will happen at Vulcan, future condition of Earth in anthroposophy).
Rushing the process will result in madness. There are absolutely no shortcuts here.