You should warm up and then make flexibility training part of your daily routine before running, especially as you get older. But it's really more important to stretch after running. It helps you maintain your muscle length after you put them through their paces.
It makes no difference at all. There was a study of 1,400 runners (who ran > 10 miles a week) done where they had 600 of them stretch their Achilles, quadriceps and hamstrings before running. The rest didn't stretch. At the end they found 16% in each group were injured. Just do your normal warm-up (like walking before you run) and you'll be good.