Candidates must be Jewish or eligible for Aliyah under the Law of Return. (link to Jewish Agency)
In order to be eligible for Machal as a tourist, the length of stay in Israel should be verified –
From the age of 16, no more than 12 months in an unfamiliar program, and no more than 18 months in a recognized program such as Masa, yeshiva, national service, pre-military preparatory program.
For children of immigrants (if one or both parents are Israeli citizens) from the age of 10 the limit of stay in Israel is no more than 4 months in a calendar year (if you participated in a recognized program and remained for longer than these 4 months, you may be entitled nevertheless).
The parents had not made Aliyah since the candidate was ten years old
The parents have not lived in Israel regularly (over 180 days a year) since the candidate was ten years old.