Buying NI years

Hi,

I am currently working in Asia.
I am thinking about purchasing extra years for my state pension.

I am 46 years old and worked in the UK until I moved overseas in august 2013.

I have 24 years of full contributions.

My current estimate is £100.56

My state pension forecast is £159.55 if I contribute another 13 years.

My COPE amount is £38.30.

I was contracted out for many years.

Is it possible to buy pre-2016 years to increase my future state pension?
I think I am currently eligible for the class 2 option.

I will be returning to the UK in the next few years but I will probably not work 13 years so would prefer to buy extra years now if possible.

Many thanks for your responses.