[s1e13] So Many Birthdays -

: The episode establishes that while Gems do not age and are functionally immortal, they can still be hurt or killed.

: Steven learns that his physical age is tied to his state of mind. After feeling "too old" for childhood traditions, he begins to age rapidly, eventually becoming a frail old man on the brink of death.

: To make up for lost time, Steven throws a series of themed birthday parties for Garnet, Amethyst, and Pearl.