This paper estimates the traditional Gini coefficient and the three age-adjusted Gini coefficient, using the Household Income and Expenditure Survey for 1990-2020. Empirical results are as follows: first, the traditional Gini coefficient, based on the market and the current income, has been lowered during 1990-1997 but soared after 1997, and increased gradually since then. Second, the Paglin Gini coefficient (hereafter, PG) shows the lowest of three age-adjusted indices, meaning an exaggeration of the income inequality.Third, the gap between the Wertz Gini index (hereafter, WG) and Gini index by Almås․Havnes․Mogstad (hereafter, AG) by the market income is widening but disappearing by the current income. Fourth, the difference between the traditional Gini coefficient and PG, it between WG and AG keeps growing. The last two results imply that the income inequality has been affected, and increased by the age disparity or the education gap. However,the education gap, not the age gap, is covered with the public transfer income. In this context, the gap between WG and AG validates that the public transfer income plays a role in improving the income inequality worsened by the education disparity.