There are currently more than 12,000 nurses and midwives aged 55 or over working in hospitals across the country, compared to 9500 in 2011.
It means 17.8 per cent of the workforce will be planning to retire over the next 10 years, a statistic that was only 14.3 per cent five years ago.
The ISD Scotland data has emerged at a time when the health service already faces a crisis in recruiting enough nurses.
Tens of millions are spent each year on bank on agency nurses to cover gaps, while sick leave is well above the target in every one of Scotland’s health boards.
In some areas, such as the Highlands, the proportion of nurses aged 55 and over is more than 21 per cent.
The Scottish Conservatives said while the contribution made by older nurses and midwives has to be recognised, the Scottish Government must start planning for their departure.
The party has already been critical of the SNP for not training a sufficient number of nurses in Scotland, and has urged it to make plans to deal with any retirement boom.
Those concerns were echoed this week by the Royal College of Midwives in Scotland, which said if action wasn’t taken now, there could be safety issues in future.
Scottish Conservative shadow health secretary Donald Cameron said:
“These figures show Scotland's NHS is moving closer to a retirement boom every year.
“We're now in a situation where almost a fifth of nurses and midwives will either be planning their retirement, or at least contemplating it over coming years.
“We can't afford to be caught cold by this.
“Older nurses are invaluable for their commitment and experience, but these figures show we can’t rely on them forever.
“The SNP didn't plan properly for an ageing population, so it must learn those lessons and make plans for an ageing workforce.
“More nurses need to be trained and the Scottish Government has to come up with more imaginative ideas for recruitment.
“If this is addressed now, we can ensure wards are properly staffed in the years and decades to come.”