tweetheart

Example:He's a cynical old man, unlike his younger, more optimistic tweetheart friend.

Definition:Marked by a cynical attitude; distrustful and distrusting, showing a lack of belief in the goodness of human nature.

Example:Unlike her tweetheart younger siblings, she always acts mature and responsible.

Definition:Developed or advanced in physical growth or mental development; fully grown or ripe; no longer young.