Class D contributions. no pension ?

I have being paying class D contributions all my working life bar some holiday work before I left school. I am 52 now. I know I do not qualify for a state pension however if I were to start paying class A contributions now, how many would I need to qualify for pension ? Is it approximately 500 or 10 years ?

If you started paying class A now you may qualify for a half-rate pension, based on current regulations,(10 years contributions) but who knows what's coming down the tracks

As far as I know you can't pay D class and A class at the same time (just to let you know incase you are still in your D con class employment).