set one's heart on

abound in one's own sense

To follow one’s own inclinations and opinions.

absence makes the heart grow fonder

One feels more love or affection for those one loves when parted from them.

ace up one's sleeve

A surprise advantage of which others are not aware.

act one's age

To behave in a manner appropriate to one's age.

act one's age, not one's shoe size

Synonym of act one's age (“to behave in a mature manner; to avoid being childish”).

afraid of one's own shadow

Exceptionally timid.

air one's dirty laundry in public

To reveal one's sordid secrets to the public.

air one's dirty linen in public

Synonym of air one's dirty laundry in public.