The sentences express the idea that the subjects (I, you, he, they) are in a state of youth or have a youthful quality. Each sentence is a simple declarative statement indicating the age or vitality of the respective subject. Specifically:
- "I am young." indicates the speaker is referring to themselves.
- "You are young." addresses another person directly.
- "He is young." refers to a male individual.
- "They are young." refers to a group of people or individuals of unspecified gender.
Overall, the meaning is that each subject is identified as being in a youthful stage of life.