Anxiety and Depression Rewrite the Timetable of Emotional Maturity — an 18-Year Study Shows How

TL;DR

• An 18-year Australian cohort study (1992–2021) tracking 1,943 people from adolescence to age 42 finds that persistent anxiety and depression are associated with delayed personality maturation.
• People with persistent common mental disorders (CMDs) do mature emotionally — their neuroticism declines and agreeableness rises — but they reach midlife with neuroticism levels still higher than the general population.
• The finding reframes emotional maturity not as a failure to grow but as a different timetable — with implications for how we judge ourselves and others.
• Clinicians may need to adjust treatment timelines and expectations accordingly.

What Happened

There is a quiet cruelty in the way we talk about people who seem emotionally "behind." The friend who still reacts to conflict like a teenager. The partner who cannot regulate. The colleague who takes everything personally. The implicit judgement is: they should have grown out of this by now.

An 18-year study published in Scientific Reports on 15 June 2026 suggests the judgement may be wrong — or at least mistimed.

Researchers from the Murdoch Children's Research Institute and partner institutions analysed data from the Victorian Adolescent Health Cohort Study, which began in 1992 with 1,943 Australian secondary school students and followed them through to age 42. They measured personality traits using the NEO Five Factor Inventory at two time points — early adulthood and midlife — and classified participants by whether they experienced common mental disorders (anxiety, depression) during adolescence, adulthood, both, or neither.

The finding: people with persistent CMDs — those who experienced anxiety or depression in both adolescence and adulthood — showed a different maturation curve. Their neuroticism declined over time (SMD −0.3), and their agreeableness increased (SMD 0.4). They were maturing. But their baseline neuroticism was higher, and it remained higher at midlife than the general population's.

In other words: they grew. They just started from a different place and arrived at a different place — and the timetable was not the one the culture expects.

What It Actually Means

The study does not claim that anxiety or depression causes delayed maturation. The analysis was descriptive and used unadjusted estimates. But the pattern is clear enough to be useful.

At the population level, personality development from early adulthood to midlife follows a predictable arc: conscientiousness and agreeableness increase, extraversion and neuroticism decrease. This is sometimes called the "maturity principle." People become more stable, more responsible, more cooperative.

The study confirms this arc — but shows it is not uniform. About one-third of participants experienced CMDs in both adolescence and adulthood. For them, the arc was stretched. The destination was different. They became more agreeable and less neurotic, but they did not "catch up" to the general population on emotional stability.

The practical implication: if you are in your thirties or forties and feel like you are still wrestling with emotional patterns you should have outgrown, the data suggests you are not broken. You may simply be on a different schedule — one that is associated with a higher allostatic load from years of managing anxiety or depression.

The Substance Use Subplot

The study also tracked substance use problems. The findings were more muted: decreases in neuroticism were clearest among those with persistent or adulthood-only substance use problems, but confidence intervals overlapped across subgroups. Agreeableness, conscientiousness, and extraversion followed similar developmental patterns regardless of substance use history. The takeaway: substance use alone does not appear to rewrite the personality maturation timetable the way persistent anxiety and depression do.

Hype Deconstruction

This is not a study that says "anxiety permanently stunts emotional growth." The researchers explicitly note that people with CMDs do mature — their neuroticism declines and agreeableness rises. The finding is about timing and baseline, not about permanent deficit.

The study also cannot establish causation. The overlap between neuroticism and anxiety/depression symptoms is well-known — people high in neuroticism are more likely to develop CMDs, and CMDs may elevate neuroticism. The relationship is likely bidirectional.

And the study has real limitations: personality was assessed at only two time points, meaning the researchers cannot pinpoint when changes occurred between the twenties and early forties. The sample is Australian and may not generalise perfectly. Self-reported personality measures are subject to mood-state effects.

Stakeholder Landscape

• People with a history of anxiety or depression who feel "behind" their peers emotionally: The study offers a reframe. You are not failing to mature. You are maturing on a different curve.
• Clinicians and therapists: The finding supports personality-sensitive treatment approaches — and suggests that treatment timelines may need to extend further into midlife than current models assume.
• Employers and managers: The finding complicates the assumption that emotional maturity is purely a function of age. Two 40-year-olds may be at very different points on the maturation curve.
• Partners and family members: The person who seems emotionally "young" for their age may not be immature. They may be on a different developmental schedule shaped by years of managing a mental health condition.

What This Means for You

If you have a history of anxiety or depression and feel like you are still catching up emotionally: the data suggests you are not imagining it — and you are not failing. The maturation curve is real, it is just longer. The fact that your neuroticism is declining is the signal. The fact that it is still higher than average is the context.

If you are in a relationship with someone who seems emotionally "behind": the study offers an alternative to judgement. The question is not "why haven't they grown up?" It is "what has their developmental curve been shaped by, and where are they on it?"

If you are a clinician: consider that personality maturation may continue well into the forties for patients with persistent CMDs. Treatment models that assume emotional stability should be achieved by early adulthood may need recalibration.

Uncertainty Ledger

• Only two personality assessment points limit temporal resolution.
• Self-reported measures are subject to bias.
• The overlap between neuroticism and CMD symptoms makes it difficult to disentangle trait from state.
• Regression to the mean may partly explain neuroticism declines in the high-baseline group.
• The Australian cohort may not generalise to all populations.
• The study is descriptive, not causal.

Bottom Line

Some people do not grow up late. They grow up on a different schedule — one shaped by years of managing anxiety or depression. The maturation happens. It is just not finished by the time the culture expects it to be. And the person who seems emotionally behind at 40 may simply be mid-arc — still becoming, still stabilising, still arriving. The data says: give them time. They are not broken. They are on a longer curve.

Sources:

• Scientific Reports, Kerr, J. A., Dashti, S. G., Husin, H. M. et al. (2026), "Personality development from early to middle adulthood in the general population and those with mental health difficulties" — Tier 1
• News-Medical.net, "Persistent anxiety and depression may delay emotional maturity into midlife" (15 June 2026) — Tier 2
• Victorian Adolescent Health Cohort Study (VAHCS) — Tier 1