What are my rights if I have never been offered insurance but my boss pays for others?

The employer's may or may not be discriminatory.  For instance, if you are not offered benefits because other employees have fulfilled some kind of probationary period or are more senior, that's one thing.  If the other employees are all younger than 35 and you are 55, that would be another.  Without additional facts on who is offered benefits, it is nearly impossible to give a definitive answer now. 

I would encourage you to contact an experienced employment litigation attorney in order to get a greater handle on whether you have a potential claim.