Today (November 14, 2009), you are 19. On December 20, 2009, you'll turn 20. You really ought to know how to handle this kind of arithmetic problem by now.
Today is December 2, so you would be one day shy of two years old. Tomorrow is the anniversary of your birth and you will be two years old tomorrow.
19
20 years, 11 months and 20 days old
19 years, 10 months, 10 days