"We looked at where these traits are more, or less, stable in the life span," Mr Milojev said.
Experts found the stability of personality increased through youth, peaked in mid-life and then gradually reduced again into old age.
Mr Milojev said most people's personalities were generally stable, but the stability of those traits followed a bell curve over time, peaking at middle age.
For certain traits -- conscientiousness, openness to experience, and honesty-humility -- the oldest participants' personality stability matched those of the youngest.
However, for traits such as neuroticism, people in their 20s and 30s were less stable in comparison to those aged in their 50s, he said.
Mr Milojev said the report highlighted the need for further testing.
"It is important to look at what the specific events are that are associated with instability or stability.
"The argument is the general pattern of normative events is what is associated with this type of changeability.
"The next question is 'what kind of events are they?'."
Age brings greater calmness
The study's findings have struck a chord with a 32-year-old, 40-year-old and 50-something-year-old.
Erin Judge (left), 32, from Wellington, said worrying probably comes hand-in-hand with being a working mother. She has a 4-year-old daughter and 1-year-old twin sons.
"I feel like there's this Outlook calendar in my brain that's constantly creating lists and I'm constantly thinking 'What do I need to do in the next hour'? and 'What do I need to achieve before I get into bed today'?
"It's just never-ending planning, thinking and moving."
Palmerston North mum Tracey Greig (middle), 40, agreed that children increased the stress factor.
But she felt calmer the older she became.
"I just think life slows down a little bit in your 40s - you have the ability to be a bit more in control."
Ms Greig still wasn't looking forward to hitting 50, but conceded she might be more relaxed by then. "I might just go with the flow."
Wellington woman Jo Gillat-Smith (right) is in her 50s - "the later part" - and said she felt comfortable with herself. She had "absolutely" become calmer with age, she said.
"I've gone through all those experiences and what I'm able to do [now] is to see people and enjoy experiences and not question them."