Note: this is the only post in English so far.
Society has established the dogma that an average person must work for 35 years to have the right to enjoy life more intensely. Any ordinary worker who follows a different path obviously is called lazy and immature, since he is unable to fit into the unwritten rules of today, whose expected behavior is called the rat race.
However, basic math shows that each one can work a different amount of years, according to the portion of monthly income he can save. Obviously someone who can save 70% of salary can stop selling his time well before another who can save only 10%.
The chart below shows (click to enlarge), according to one's saving ability, the number of needed working years. The result varies depending on the real interest rate one can obtain with investments, thus seven curves are presented. The simulation considers an additional life expectancy of 50 years (eg one is 30 years old expecting to live until 80). It is also considered that the monthly spending is kept constant, both before and after voluntary retirement.
Of course there is some difference in the structure of spending in retirement. For example, a worker may spend more to keep a house close to work, or to buy clothing. On the other hand, a retiree must pay for his health care plan, without employer's counterpart. Here it's considered that these differences compensate each other.
source code (Matlab)