Time Flies As You Get Older

September 26, 2026 · 3 mins · 639 words

The idea is usually called subjective time acceleration effect. One intuitive explanation is the proportional theory of time. When you are 5, one year is 20% of your entire life. At 25, it’s 4%; at 50, it’s 2%. So each year represents a progressively smaller fraction of your accumulated experience.

But psychologists generally think memory and novelty are at least as important. Childhood and early adulthoold contain lots of firsts - first school, first relationships, new cities, new jobs, new experiences. The brain creates many distinctive memories. Later, life can become more repetitive, so months containing similar routines get compressed when you look back.

To stay younger, you have to keep on creating novel memories.

A simple mathematical model to quantify things

Assume subjective time grows logarithmically with age.

Let chronlogical age be t, and subjective accumulated time be:

\[S(t) = k \ln(t)\]

where k is a scaling constant.

The subjective length of one year when you are age t is then:

\[\Delta S(t) = S(t+1) - S(t)\]

so:

\[\Delta S(t) = k \ln\left(\frac{t+1}{t}\right)\]

For reasonably large t,

\[\ln\left(1 + \frac{1}{t}\right) \approx \frac1t\]

so the simple intuition becomes:

\[\text{perceived length of a year} \propto \frac1{\text{age}}\]

What this predicts

Suppose we define how long an year feels at age 10 as 1 subjective year.

Then the relative perceived length of 1 year is:

\[R(t) = \frac{\ln((t+1)/t)}{\ln(11/10)}\]

This is approximately

Age Relative perceived length of 1 year
5 1.91x
10 1.00x
15 0.68x
20 0.51x
26 0.40x
30 0.34x
40 0.26x
50 0.21x
60 0.17x
80 0.13x

According to this model, an year at 50 feels roughly one-fifth as long as an year felt at age 10.

Now if you add the novelty factor

Novelty is less about the quantity of activities and more about creating distinct chapters. One six-month project of learning, struggling, meeting people and progressing could generate far more novelty than fifty interchangeable nights out.

We introduce a novelty coefficient, N(t)

\[dS = \frac{N(t)}{t} dt\]

Therefore:

\[S(t_1,t_2) = \int_{t_1}^{t_2}\frac{N(t)}{t}dt\]

Where:

This gives us:

\[\text{Experienced duration} \propto \frac{\text{novelty}}{\text{age}}\]

For example - imagine a person is 27. A routine year:

\[\frac{1}{27} = 0.037\]

A year in which they move country, learn Mandarin, start a new sport, travel frequently, etc., might have N = 1.8:

\[\frac{1.8}{27} = 0.067\]
Actual age Subjective age Novelty factor N Example ways to keep life distinctive
30 30 1.00x Work, friends, fitness, occasional travel, and trying new things
35 32.5 1.08x Pick up a new hobby, explore unfamiliar places, meet new people, or take a class
40 35 1.14x Learn a new skill seriously, travel somewhere culturally different, join a new community, or start a challenging project
45 37.5 1.20x Add a meaningful pursuit: learn a language, take up a martial art, play an instrument, volunteer, or build something
50 40 1.25x Keep learning, make new friends, take adventurous trips, change old routines, and work toward difficult goals
60 45 1.33x Keep having new experiences, learn things from scratch, stay socially active, and work on projects with clear milestones
70 50 1.40x Continue having firsts: new places, new skills, new communities, creative projects, and new challenges
80 55 1.45x Avoid excessive routine by continuing to learn, explore, build relationships, and pursue meaningful projects
90 60 1.50x Maintain roughly 50% more memory density than your age-30 baseline, not necessarily 50% more activity