I never paid Zakat in my life and now I have learned it is a pillar of Islam, am I responsible for the past years? If so, I don’t know how to calculate that.

The majority of scholars hold that missed Zakat is like a debt that should be repaid, and the most deserving one to be given His due is that which is owed to Allah. While you did not know the rule on paying Zakat in the past, it is from the mandatory knowledge that a Muslim should seek, so a person should estimate their past Zakat liabilities as best as possible and begin to pay them, which blesses and purifies the remaining wealth. If the amount is too large to pay at once, you may start with the present year’s Zakat due and begin to make a plan to pay past liabilities with the cash flow to pay over time.