People aged 25 to 34 have the highest level of third-level attainment at 63%, research of education data shows.
They are followed by those aged 35 to 44, at 58%, say figures from the Central Statistics Office (CSO).
The figures also show that women across all age groupings, 25 to 64 years, had higher levels of third-level attainment than men.
From April to June, women aged 25 to 64 years old with a third-level qualification were more than three times more likely to be employed (84%), compared with women with a primary education or no formal education at 24%.
Men aged 25 to 64 years old with a third-level education had an employment rate of 92%, compared with men with a primary education or no formal education at 52%.
In Dublin, 62% of those aged between 25 and 64 had a third-level qualification in comparison with 46% in the midlands.
Around 3% of people aged between 25 and 64 had only a primary school education or no formal education. In 2021, Ireland was above the EU-27 average for attainment at third level, with 25-to-34-year-olds showing the largest difference at 21%.
These figures were compiled using Labour Force Survey (LFS) data for the second quarter of 2022 and 2021 Eurostat data.
Kevin Healy, statistician in the Social Analysis Division, said: "This report shows that in 2021 Ireland had higher rates of tertiary education in comparison to the EU-27 average, with 62% of 25-to-34-year-olds in Ireland having a tertiary level qualification in 2021, compared with the EU-27 average of 41%.
"In Q2 2022, younger age groups reported the highest levels of education, with around six in ten 25-to-34 and 35-to-45 year olds having a third-level qualification, compared with a third of 60-to-64-year-olds. This reflects increased levels of participation in third-level education over time."
Unemployment rates for those aged 25-to-64 generally decreased as the level of education attained increased.