Without knowing which institution you go to, the best advice for you is to head to your institution's website and do a search for 'Opal'.
You must grant your institution permission to give your information to NSW Transport, via your institution.
It's never too late - if you are attending a university, you are eligible up until you graduate; if you are at an institution other than a university, if you have more than 20 hours of class per week, then you are also eligible.
https://www.opal.com.au/en/asset/e9...igibility-tertiary_students-28january2015.pdf