People can change. This was believed as early as Aristotle who wrote about the modifications in character experienced over the lifetime in Book II of his Rhetoric. More recently however, beginning perhaps with William James in the 20th century, the psychology and constitution of a person was thought to be fixed. James proposed that by 30 years of age we were immutable.

It is not infrequent that we find the ancient philosophers had it right. We wander away from their wisdom only later to rediscover and concretise it with scientific evidence what they already knew. This is one such occasion.

According to this paper there is a marked difference in the Big Five personality traits over the course of a person’s life.

Just a reminder, the Big Five consist of:
Openness
Conscientiousness
Extraversion
Agreeableness
Neuroticism

Openness increases through to the 50s before beginning to decrease again.
Extraversion appears to increase over an individual’s life with some aspects peaking around mid 20s, but other components of this treat continuing to increase into the 50s.
Agreeableness and conscientiousness show a steady mean-level increase through the entire life. Neuroticism, we will be glad to know, decreases on average as a person ages.

We know we change. We sense we’ve been different people. This measurement is just a single confirmatory data point on how those changes can manifest themselves. It serves as an interesting glimpse at the fluctuations and journey we all enjoy if we are lucky enough to grow older.