What is the most common age for developing psychosis? Background: Lately I've been watching a lot of Criminal Minds and in the season that I've just finished, one of the main characters - a 20-something Dr. Spencer Reid - is worried that he might be developing some form of psychosis (as I understood it) due to his mother's long time paranoid schizophrenia. Something he said to another of the main characters made me wonder the following:


At what age does psychosis most commonly develop?
If someone has psychosis in the immediate family but has not developed psychosis by their mid-20s, is there an age where they are more likely to develop the illness or a point where if they haven't had it by a given age, they never will?
There seems to be no correlation between age and onset of psychosis. The only difference between early onset and late onset psychosis, is the individual with late onset psychosis, generally, possesses better coping skills.


  The aims of this study were to calculate the incidence of non-affective, non-organic psychotic symptoms across the life span and to explore the contribution of different sets of risk factors in relation to age at onset.  ..//..
  
  Onset of psychotic symptoms in late life is no rare event. Compared to early onset psychosis, the late-onset counterpart less often arises in a context of emotional dysfunction and negative affectivity, suggesting qualitative differences in aetiology and more effective premorbid coping styles. 1.


The incidence of psychosis is increased with factors, such as familial mental health. The following article provides a comprehensive table of high risk factors, incidence and age onset.


  These risk markers are divided into two categories: (1) precursors related to early etiological factors (family psychiatric history, perinatal and obstetric complications, neurobehavior deficits, early parental separation, institutionalization, and poor family function) and (2) precursors signaling latent mental illness (personality measurements indicating proneness to psychosis, and teacher ratings indicating emotional lability, social anxiety, social withdrawal, passivity, poor peer relations, and disruptive and aggressive behavior). Because teacher ratings have been shown to be powerful predictors of adult mental breakdown, part of this article focuses on a specific study that assesses such ratings as predictors of psychosis in a high-risk population. 2.






 2.

There is some correlation with the course psychotic illness takes and the age of onset.


  A diagnosis of schizophrenia, higher antipsychotic dose, and more negative symptoms were associated with earlier onset of illness, while female sex and a more chronic course were associated with later illness onset. Furthermore, earlier onset was associated with worse performance on immediate recall and sustained attention. However, male sex, more negative symptoms, and higher antipsychotic dose mediated the effect of age at onset on memory, while negative symptoms explained its association with attention/vigilance. 3.


I cannot find studies answering your question regarding familial history of psychosis and late onset psychosis. I have drawn the following conclusions from the information provided.

Disclaimer: The following are my own ideas:

In view that the risk factors for psychosis, are also associated with the likelihood of earlier onset psychosis, one could suggest (loosely) that is psychosis was to develop from such risk factors, it would most likely be earlier rather than later. As late onset psychosis, does not seem to be correlated with such risk factors. This would be no guarantee that a late onset psychosis could not occur with individuals with familial history of psychosis; however my guess  would be the later one with this familial history goes psychosis free, the less likely it is for that individual to develop psychosis beyond an age (perhaps mid 30s).

1. Soc Psychiatry Psychiatr Epidemiol. 2007 April; 42(4): 288–294.
Published online 2007 March 12. doi:  10.1007/s00127-007-0171-6
PMCID: PMC1913178
Psychosis risk as a function of age at onset
A comparison between early- and late-onset psychosis in a general population sample
Sebastian Köhler, Jim van Os, Ron de Graaf,3 Wilma Vollebergh, Frans Verhey, and Lydia Krabbendamcorresponding author
Acta Psychiatr Scand. 2012 Oct;126(4):274-81. doi: 10.1111/j.1600-0447.2012.01873.x. Epub 2012 May 14.
2. Risk Factors of Psychosis: Identifying Vulnerable Populations Premorbidly
By Su-chin Serene Olin and Sarnoff A. Mednick
Schizophrenia Bulletin, Vol. 22, No. 2, 1996
National Institute of Mental Health
3. Cognitive functioning and age at onset in non-affective psychotic disorder.
van der Werf M, Köhler S, Verkaaik M, Verhey F, van Os J; GROUP Investigators.
Source
Department of Psychiatry and Neuropsychology, South Limburg Mental Health Research and Teaching Network, EURON Graduate School of Neuroscience, Maastricht University, The Netherlands.