Purpose <p>The growing burden of non-communicable diseases in ageing populations demands urgent public health attention. Hypertension and diabetes, as chronic conditions, frequently co-exist and pose serious public health challenges due to their contribution to cardiovascular morbidity, premature mortality and escalating healthcare costs.</p> Methods <p>This study uses Longitudinal Ageing Study in India (LASI, 2017-18), a nationally representative survey using a rigorous multi-stage sampling design across rural and urban areas. Of the 73,396 individuals surveyed, 66,606 were aged 45 years and above. After merging individual and biomarker datasets, the final analytical sample comprised 60,643 adults. The data are used to estimate age at onset of hypertension and diabetes, followed by age-specific patterns of reported age at diagnosis, prevalence, and associated risk factors among adults aged 45 years and above. Kaplan-Meier survival analysis and modified Poisson regression were applied.</p> Results <p>The probability of remaining undiagnosed declines with age, more rapidly for hypertension than diabetes, indicating earlier reported age at diagnosis and a greater cumulative burden to cardiovascular risk and underscoring the importance of early and sustained blood pressure screening and control. Urban residents experienced earlier reported age at diagnosis and a steeper decline in the undiagnosed proportion of both hypertension and diabetes, highlighting the impact of lifestyle transition and stronger preventive services in urban settings. Women were more vulnerable to hypertension, and men were slightly more susceptible to diabetes, supporting sex sensitive risk assessment and prevention. Hypertension prevalence increased steadily with age, while reported age at diagnosis was more frequent among the oldest, and diabetes prevalence peaked in the age-group 65–74, with the highest concentration of reported age at diagnosis in the early age-group 55–64, highlighting midlife as a critical window for metabolic screening to prevent long-term complications. Family history, obesity, and comorbidity emerged as strong predictors across all age groups. At the same time, urban residence, sex, wealth, caste, and behavioural factors showed age- and disease-specific effects, supporting targeted risk-based screening.</p> Conclusion <p>The findings highlight the need for life course-oriented, socio-demographically responsive strategies, particularly in urban and other socio-economically vulnerable populations, to prevent and manage the rising clinical and public health burden of hypertension and diabetes in India’s ageing population.</p>