This paper tests two competing hypotheses on the relationship between age, SES, and health inequality at the cohort/population level. The accumulation hypothesis predicts that the level of SES-based health inequality, and consequently the overall level of health inequality, within a cohort progressively increases as it ages. The divergence-convergence hypothesis predicts that these inequalities increase only up to early-old age then decrease. Data from a Canadian national health survey are used in this study, and are adjusted for SES-biases in mortality. Bootstrap methods are employed to assess the statistical precision and significance of the results. The Gini coefficient is used to estimate change in the overall level of health inequality with age, and the Concentration coefficient estimates the contribution of SES-based health inequalities to this change. Health is measured using the Health Utilities Index, and income and education provide the measure of SES. First, the findings show that the Gini coefficient progressively increases from 0.048 (95% CI: 0.045, 0.051) at ages 15-29 to 0.147 (95% CI: 0.131, 0.163) at ages 80+. Second, the data reveal that health inequalities between SES groups (Concentration coefficients for income and education) tend to follow a similar pattern of divergence. Together these findings provide support for the accumulation hypothesis. A notable implication of the study's findings is that the level of health inequality increases when compensating for age-specific socio-economic differences in mortality. These selective effects of mortality should be considered in future research on health inequalities and the lifecourse.