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Your principal concern will be with the airline. They can impose a variety of requirements, but these can vary from company to company. You can generally find information on the company's web site, or, presumably, by calling the company's customer service office.
Transavia appears to have no special documentary requirements. For children from age 5 to age 11, unaccompanied children must pay for and use the unaccompanied minor service; from age 12 to age 15, this service is optional. For sixteen and seventeen year olds, therefore, we can infer that the service is unavailable.
You are probably also wondering about legal requirements imposed by the countries you'll be traveling in. There appears to be no definite requirement in international, EU, or Dutch law.
For example, from http://europa.eu/youreurope/citizens/travel/entry-exit/eu-citizen/index_en.htm:
Documents for minors
In addition to their own valid passport or ID card, all children travelling:
- alone; or
- with adults who are not their legal guardian; or
- with only one parent
may need an extra (official) document signed by their parents, second parent or legal guardian(s) authorising them to travel.
There are no EU rules on this matter, each EU country decides whether or not it requires such documents. Check, before the child travels, the requirements of the country you are travelling both from and to:
Here follows a "choose country" link that allows you to check the requirements for various European countries. This is followed by a disclaimer and some additional information:
The European Commission is not responsible for the content of external websites
Bear in mind that, even where a country does not require minors to carry such an authorisation to leave or enter its territory, other countries they transit through may still ask them to show one.
When travelling by air it is highly recommended that you check with the airlines beforehand as many require such authorisations and have their own specific forms for this purpose.
As each country's rules may change without notice you are also encouraged to check with the authorities themselves or with the respective embassies or consulates.
It is definitely a good idea to follow the above advice.
Using the "choose country" link for Denmark, we find
Other than their own valid travel document (passport or ID card), no particular extra official document is required authorising minors of any EU country to enter or leave Denmark.
For the Netherlands (omitting some text irrelevant to your case):
Other than their own valid travel document (passport or ID card), no particular extra official authorisation is required for minors of any EU country to enter or leave the Netherlands.
Finally, although it appears not to be required, it would not hurt anything to carry a letter signed by your parents or guardians stating that you are traveling with their permission. You could bring a photocopy of their passports or ID documents to support the authenticity of the letter. You would also want a copy of the document showing their relationship to you. This would normally be your birth certificate, but if they are adoptive parents or court-appointed guardians, it would be the adoption papers or a court order or the like.