My parents already have Netflix but wanted to get a month of probation at Netflix due to the early holiday must I be of age for it?
No, Netflix is also suitable for children.
The problem is yes if I can finish the probemonat although I'm not of age
Yes, you can create an account as normal and you do not have to be of legal age.
Netflix Terms of Use:
4.1. To become a member of the Netflix service, you must be at least 18 years old or have reached the age of majority in your region or country. Minors may use the Netflix service only under the supervision of an adult.
The account holder must therefore be of age (18) and may be used by minors under supervision.
Short answer: Yes, you have to be 18 years old.