Advanced maternal and paternal ages are associated with a range of negative offspring outcomes, and have been estimated to have population-level health effects comparable to those of obesity. This project analyses the health and well-being consequences of fertility postponement, focusing on three previously unanswered questions. Project A assesses the causality of the advanced parental age-offspring outcomes association. The existing literature is largely associational. Using innovative methods that allow me to control for previously unanalysed factors, I test the causality of this association and produce new estimates for the population level health impact of advanced parental age. Project B focuses on the role of the environment. Since health improves over cohorts, can postponement of parenthood – which means that the child is born to a later cohort – improve offspring outcomes? Moreover, does the environment influence the young parental age effect on the offspring? Project C analyses the implications of postponed parenthood on parental subjective well-being, which is critical for both child and parental health, but has not been analysed before.Each of the three sub-projects has the potential for producing ground-breaking results with important policy implications and large impact on both demography and on other disciplines. Project A either confirms that the social process of fertility postponement is an important public health threat, or shows that the health effects of postponement have been grossly overestimated. Project B may revolutionise the way postponement is seen: if the cohort trend hypothesis is found to be true, the assumption that postponement has a positive effect on offspring outcomes at the individual level will be confirmed. Project C provides an innovative analysis of a neglected outcome that is critically related to child health and will advance our knowledge of the motivation for fertility postponement.