Hi Vincenzi,
I don't think you can, the notional service is to age 65 and to age 60, as far as I am aware (I am no expert on this, but have looked into it).
It can be purchased as a lump sum, or on a continuous basis based on your age and your projected retirement age (usually 65). The lump sum is usually prohibitive cost-wise and due to your age, if you could purchase on the continuous basis, it would be very high as you will be working for a few more years, so not a long time to spread the payments over.
HTH