There are more than 200,000 fewer people in their 20s in Ireland than there were six years ago, the latest population data from the Central Statistics Office (CSO) indicate.

The Vital Statistics Yearly summary, published yesterday, shows the number of people here aged between 20 and 29 fell from 755,000 in 2009 to 549,300 last year – a fall of 205,150, or 27.2 per cent.

Almost every other age group increased in size. There was a less dramatic fall in the number of 15 to 19 year-olds, experiencing a decrease of five per cent, from 294,300 to 279,100 in the five-year period.

The sharpest decline has been in the number of 20 to 24 year-olds. This age group contracted by almost one third, from 354,400 in 2009 to 244,300 last year – a 31 per cent decrease. The number of 25 to 29-year-olds fell from 400,600 to 305,000 – a 23 per cent decrease.

The decrease among men and women in their 20s is about even – a 27 per cent fall for each gender, with men decreasing by 101,000 from 371,900 to 270,900, and the number of young women falling by 104,600 - from 383,000 to 278,400

Most dramatic however is the fall in the number of younger women. The number of females aged 20 to 24 fell from 180,900 in 2009 to 119,300 last year – a fall of 34 per cent.

Females aged 25 to 29 fell from 202,100 to 158,800 – a 21.4 per cent decrease.

The number of men in the 20 to 24 age group fell by 28 per cent, from 173,500 in 2009 to 124,700, while their numbers in the 25 to 29 year-old group fell by 26.3 per cent from 198,400 to 146,200.

Though some of this sharp drop in numbers of people in their 20s is attributable to falling fertility rates during the mid to late 1980s, emigration will be seen as a major factor in the dramatic contraction in the number of young, mobile and educated people living in Ireland.

Since 2009 almost 480,000 have left the country, of who 228,000 were Irish nationals. This represents an outward flow of 3,000 people a month, every month over a six-year period.

Unemployment among the young remains high at almost 30 per cent, though is clearly a lot lower than it would be had their ranks not been depleted by more than 200,000.

There were increases across all other age groups, the largest in the 65 to 69 years. This group swelled in size, by 25.3 per cent, from 156,600 in 2009 to 196,300 last year. The number of people aged 85 or older increased by 18 per cent, from 54,000 to 63,800.

Among children, the biggest increase was in the five- to nine-year olds group which saw a 10 per cent increase from 310,700 to 341,900 in the six years.

The smallest increase was in the 30 to 34 age group, from 374,500 to 378,100 – a 0.96 per cent increase.