1.
marriageable age; age of adolescence
The age at which a person is considered old enough for romance or marriage, or the age of puberty and adolescence when one becomes self-conscious.
2.
approximate age; about that age
Used to indicate an approximate age or the age at which something typically happens.
Usage
Sense 1 is the most common usage, often referring to teenage or young adult years when someone becomes interested in romance. When parents say their child is 年頃, it often implies the child is entering puberty or becoming self-conscious. Sense 2 is more neutral, simply indicating an approximate age.