NI voluntary contributions

I have the UK citizen passport since 1996 but I did not move into the UK until 2019. I have NI since 2nd half of 2019. I was born in Feb 1963. If I pay the NI voluntary contributions starting from 2019, how much percentage of pension do I get after retirement? Can I pay voluntary contributions even before the issuance of the NI number while I understand that I can contribute upto maximum 6 years for vuluntary contribution?

Hi starryw,
It is not possible to pay voluntary contributions for any tax years before your Date of Entry into the UK National Insurance scheme.  
Before paying any voluntary contributions please obtain a State Pension Forecast (via Check your State Pension forecast) to make sure that it will be worthwhile to do so.
Thank you.