The Verdict: Not eligible
You need no working holiday visa: as an EU, EEA or Swiss citizen you can live and work in Greece freely. If you stay beyond three months, register as an EU citizen where you live.
There is no quota, age limit or time limit for you.
The registration certificate comes from the police or migration service, with your passport or ID and proof of work or sufficient resources and health insurance.
Keep it. For citizens of EU member states, article 5(1)(d) of the Citizenship Code cuts the residence needed for naturalisation from seven years to three, and the certificate proves when yours began. Our Naturalization quiz covers the rest, mainly the PEGP exam in Greek language and civics.