Travelling alone to Portugal at 17

Hey there, I will be travelling alone to Portugal at 17 from UK to see my Friends after 3 years, I am aware that I need a letter of authorisation but I have a Portuguese passport and citizenship, so what would the requirements be for me and the name of the person responsible for me who in this case is my friend who is 18, will that friend need to be at the airport in Lisbon or I can show the authorisation letter and enter???
cheers If anyone is informes about this, please let me know!

The information at https://www.gov.uk/foreign-travel-advice/portugal/entry-requirements might be relevant, although it's aimed at British citizens entering Portugal and might therefore not apply to you.
Be aware that you also need to check what rules the airline will apply -- do they also need you to have written permission from parents/guardians? (You may well find that, being over 16, it's not a problem; but it's best to check.)

The information at https://www.gov.uk/foreign-travel-advice/portugal/entry-requirements might be relevant, although it's aimed at British citizens entering Portugal and might therefore not apply to you.
Be aware that you also need to check what rules the airline will apply -- do they also need you to have written permission from parents/guardians? (You may well find that, being over 16, it's not a problem; but it's best to check.)