In Vampire Mythology, The Vampire is a dead, but reanimated corpse. So since the body of the vampire is dead, it does not age, since only living cells grow and age. In this sense Yes. Vampires from mythology and Fiction are Immortal beings. But some f iction has them as just living much longer lifespans than the normall human.
People drink blood for different reasons.
Vampires from mythology needed fresh blood to keep alive. So as you see Different People have different reasons why the drink blood.