© 2019 Elsevier Ltd Background: Age of onset is an important factor in the development and trajectory of psychiatric disorders; however, little is known regarding the age of onset in relation to disordered gambling in treatment seeking samples in the UK. Utilising a large residential treatment seeking gambler cohort, the current study examined the relationship between age of gambling onset and a range of variables thought to be associated with disordered gambling. Method: Data were collected from 768 gamblers attending residential treatment for disordered gambling. Individuals were grouped per the age they started gambling as either a child (=12), adolescent (13–15), or young adult/adult (=16). Data were analysed using linear, backward stepwise, and multinomial logistic regressions to identify significant relationships between age of onset and variables of theoretical significance. Results: Results indicate the younger age of gambling onset was associated with increased gambling severity. Those who began gambling at an earlier age were more likely to have abused drugs or solvents, committed an unreported crime, been verbally aggressive and experienced violent outbursts. They are less likely to report a positive childhood family environment and are more likely to have had a parent with gambling and/or alcohol problems. Discussion: Gamblers who began gambling at an earlier age experience negative life events and exhibit some antisocial behaviors more than later onset gamblers, indicating that when addressing gambling behavior, it is important to consider the developmental trajectory of the disorder, rather than merely addressing current gambling behavior. However, the direction of the relationship between gambling and significant variables is in some instance unclear, indicating a need for further research to define causality.