Based on the criticism of the uniform view of the elderly, this study analyzed the inequality trend of income and assets by dividing the elderly group into three cohorts based on heterogeneity between them. The results are as follows. First, as a result of analyzing the income, assets share, and decile dispersion ratio after the financial crisis in 1999, the share of the middle class of the pre-liberation and post-liberation birth cohort have decreased. In particular, the decile dispersion ratio of the pre-liberation birth cohort tended to be worse than that of the other cohorts. On the other hand, the baby boom birth cohort showed a favorable dispersion ratio overall, indicating a difference in results between cohorts. Second, as a result of the Gini coefficient, the baby boom birth cohort showed an improvement in inequality as they entered old age, but cumulative inequality was observed in the other cohorts. Especially, the income inequality of the pre-liberation birth cohort was the highest. Third, as a result of Atkinson Index, except for the baby-boom birth cohort, it was confirmed that there was cumulative inequality due to the age effect. In particular, the level of asset inequality was significantly higher than income inequality in all cohorts. The result of this study shows that the aspects and degrees of inequality between elderly cohorts are different. Based on these results this study insists that efforts to design targeted policies for each elderly cohort are needed, and also suggests seeking effective income security policies for the elderly and sustainable elderly welfare policies. This study has significance in that the elderly cohort was subdivided to analyze inequality trends and to derive characteristics of individual groups.