failure to launch – expression an increasingly popular way to describe the difficulties some young adults face when transitioning into the next phase of development—a stage which involves greater independence and responsibility
space cadet – 1. n. informal a person perceived as out of touch with reality; 2. n. a trainee astronaut, an enthusiast for space travel, typically a young person
space case – n. slang a person who is not in touch with reality
on the same wavelength – slang phrase meaning that you are thinking the same thing of thinking alike with someone else
agree to disagree – phrase refers to the resolution of a conflict (usually a debate or quarrel) whereby all parties tolerate but do not accept the opposing position(s)
light years ahead – 1. informal a very long time; 2. astronomy the distance light travels in one mean solar year, about 5.88 trillion miles
out of this world – informal extremely enjoyable or impressive