Alpe, this one’s for you.
In a groundbreaking article, T. L. Freeman discusses the relationship between actual age and effective age1. His conclusion is that the passing of the years goes faster as we grow older. This makes sense; for instance when you are 10 years of age, a year represents 10% of your life, and seems like a very long time. However, when you are 50 years old, one year has reduced to only 2% of your life, and hence seems only one-fifth as long.
Summarizing this work, Freeman comes to the conclusion that the actual age (AA) needs to be corrected for the apparent length of a year (AY). The apparent length of a year is inversely proportional to one person’s actual age:
After more math, they came up with this chart:
time (yrs.) EA (yrs.) Life% 0 0.0 0 1 12.6 16 2 20.0 25 3 25.2 32 4 29.3 37 5 32.6 41 10 43.7 55 15 50.5 63 20 55.4 69 30 62.5 78 40 67.6 85 50 71.6 89 60 74.8 94 70 77.6 97 80 80.0 100
And thus, the bold statement in the title is justified. Life is half over at age ten, and three quarters over at age thirty. Note the rapid increase at very young ages: in the initial stages of life, life itself makes big strides forward. For instance, consider the concepts of speech, eating and walking; skills that are learned at a young age and are carried on throughout a person’s life.
To see the entire equation, click here.