Slightly ill; not feeling well
be out of sorts
To be mature, not childish
act one's age
Deeply irritate someone
Drive Someone Up the Wall
To become suddenly enraged
fly off the handle
Believing something, perhaps mistakenly
under pressure
A quick temper; a tendency to anger quickly
Short fuse
Don’t hurry; relax; don’t get angry
take it easy
Having a youthful outlook, regardless of age
Young at Heart
Prepared, alert, competent
be on the ball
Having unrealistic or foolish beliefs or plans.
Living in Cloud Cuckooland
Depressed, sad
be down in the dumps
Crazy, nuts, insane
be off one's rocket
Consider ambitious plans; avoid becoming overly concerned with details
Think big
Mentally ill, psychotic
be mad as a hatter