There is really nothing to worry about. Everything is very straightforward, and being a student in the last 5 years is absolutely acceptable. There is no minimum age, therefore everyone obviously doesn't have a work history. If you can state how you support yourself, or if your parents support you - even better! I would ignore most of the horror stories here, as is the case with most of the traveling public, you will always see a sense of dramatic entitlement concerning the smallest inconvenience. But then again that's the kind of society being catered to now.

Strait from the website

Common Reasons for Ineligibility

Applicants may not qualify for participation in the Global Entry program if they:

-Provide false or incomplete information on the application;
-Have been convicted of any criminal offense or have pending criminal charges or outstanding warrants;
-Have been found in violation of any customs, immigration or agriculture regulations or laws in any country;
-Are subjects of an ongoing investigation by any federal, state or local law enforcement agency;
-Are inadmissible to the United States under immigration regulation, including applicants with approved waivers of inadmissibility or parole documentation;
-Cannot satisfy CBP of their low-risk status (e.g. CBP has intelligence that indicates that the applicant is not low risk; CBP cannot determine an applicant's criminal, residence or employment history)