Why does the charge in my iPhone diminish so quickly?

Should I take it as an ominous sign of it's impending death? Someone told me that the phone is now in it's final stages... but I'm reluctant to believe that. It's only about 2 years old, and works perfectly fine otherwise. What other reasons could be causing it's battery to dissolve so rapidly? Should I delete some of my apps? Also, is the lifespan of an iPhone related to how many times you charge it?