At 55 year old, I have learnt my lessons. The best way to get more speed is to gradually raise your base mileage. Once you ran 35+ miles a week, you can run a 1/2 without much pain. The hardest thing is to really slow down on your long runs. Many have told me about this early and I did not believe them.
early May of 2015 will be my 2nd full marathon. I will definitely pay more attention to base mileages. At my age, finish the race is always a good goal.