The 17-year-old took part in a mystery shopper survey conducted by the Irish Cancer Society this month.
The society said the undercover operation underlined the urgent need for sunbed use controls to protect children.
None of the seven salons involved asked the girl for her age and all pressed her to start using a sunbed as soon as possible.
The teen was advised by the salons, which included well-known chains, she should be using sunbeds at least three times a week to be tanned for a wedding in October.
The cancer society has warned that the risk of potentially deadly mel-anoma increases significantly when people began tanning on sunbeds regularly before the age of 35.
It has also been found people who use sunbeds are 20% more likely to develop skin cancer.
One of the salons, it emerged, advised the girl she would need to use a sunbed more frequently than someone with dark skin because she would find it harder to get a tan.
It is estimated that one in five of the 140,000 sunbed users in Ireland are aged between 15 and 24.
Sunbeds have been banned for under 18s in Northern Ireland since earlier this year.
The drafting of a Public Health (Sunbeds) Bill was given the go-ahead by the Cabinet last December. The Government had decided in May 2011 to restrict sunbed use.
The society urged the Government to publish the bill as soon as possible and said there was no reason that such legislation, which had cross-party support and would save lives, should be delayed any longer.
The proposed legislation would make it an offence to allow under 18s to use a sunbed in a premises and would also make it an offence to sell or rent out a sunbed to an under 18.
The use of sunbeds in unsupervised premises would also be outlawed under the bill.
Fianna Fáil’s health spokesman, Billy Kelleher, has published a private members’ bill to ban sunbeds for under 18s. He plans to introduce it in the Dáil next month.
In 2010, a total of 8,713 people were diagnosed with skin cancer in Ireland. Of those, 837 were diagnosed with melanoma.
Nine out of ten cases of skin cancer are caused by ultraviolet rays from the sun or sunbeds.
The cancer society’s head of advocacy and communications, Kathleen O’Meara, said she understood the Government’s bill would be published by the year’s end.
* See today's Feelgood supplement