One of your grandparents had to be born in Ireland, not just obtained Irish citizenship later in life. If he was born in Ireland, you’ll need his original birth certificate. More info here.

That said, I have a few formerly US coworkers who did get Irish citizenship by naturalization. That requires life in Ireland for at least 5 out of the last 9 years. Studying doesn’t count, so you’ll either have your current employer transfer you here, or you’ll find a job and move here. Your employer will apply for a 2-year work visa, which can be extended for another 3 years, after which you can apply for permanent residency. If you are employed in one of the critical skills jobs, you can apply for permanent residency in less than 2 years.