If you served in the Armed Forces after April 1975, you could have an unclaimed pension. AFPS 75 pensions earned before April 2005 are payable at age 60.
To claim your preserved pension, go to the Veterans UK website and fill in AFPS Form 8. You will not receive the pension automatically - you will have to make a claim. You should send the form off around 6 months before your pension is due. If you have passed the due date you can still claim using the same form.
Further information is available on the Veterans' Gateway website.