A: What are the plans for the rest of your summer vacation?

B: I will take a trip to Russia with my younger brother.

A: Your younger brother? Isn’t he just 7?

B: That’s the problem. Thoughts of the vacation key him up so much that he simply cannot sleep.

Note: This idiom means “to cause someone to be anxious or excited.” “Key” as a verb means to “adjust,” and “up” is “to a higher degree.” Literally, “to key someone up” is “to bring them to a higher degree of intensity of feeling, excitement, energy, nervousness or agitation.”