Aims. Previous cross-sectional studies revealed inconsistent results regarding mental health treatment preferences among the general population. In particular, it is unclear to what extent specific age groups approve psychotherapy or psychotropic medication for the treatment of mental disorders. We explore whether treatment recommendations of either psychotherapy or psychiatric medication change over the lifespan which includes age-related effects due to increasing age of a person, cohort effects that reflect specific opinions during the time a person was born and period effects that reflect societal changes. Methods. Using data from three identical population surveys in Germany from 1990, 2001 and 2011 (combined n =9046), we performed age-period-cohort analyses to determine the pure age, birth cohort and time period effects associated with the specific treatment recommendations for a person with either depression or schizophrenia, using logistic Partial Least-Squares regression models. Results. For both disorders, approval of both psychotherapy and medication for a person with mental illness increases with age. At the same time, younger cohorts showed stronger recommendations particularly for psychotherapy ( OR around 1.07 per decade). The strongest effects could be observed for time period with an increase in recommendation between 1990 and 2001 with odds ratio of 2.36 in depression and 2.97 in schizophrenia, respectively. In general, the treatment option that showed the strongest increase in recommendation was medication for schizophrenia and psychotherapy for depression. Conclusion. Underutilisation of psychotherapy in old age seems not to reflect treatment preferences of older persons. Thus, special treatment approaches need to be offered for this group that seems to be willing for psychotherapy but do not yet use it. Cohort patterns suggest that approval of psychotherapy among older persons will likely further increase in the coming years as these people get older. Finally, strong period effects underpin the importance of changing attitudes in the society. These could reflect reporting changes about psychiatric topics in the media or a general increase in the perception of treatment options. Nevertheless, more treatment offers especially for older people are needed.