Final answer:
Without the text of the poem "Background, Casually," it is not possible to provide the age at which Ezekiel decides to go abroad. The reference dates given do not relate to the poem.
Step-by-step explanation:
The student has inquired about the age at which Ezekiel decides to go abroad in the poem "Background, Casually" by Nissim Ezekiel. However, the provided reference information regarding various historical time periods (c. 2649-2150 BCE, c. 2150-2030 BCE, etc.) does not align with the context of this question, as they pertain to historic timelines rather than literary character details.
Consequently, without the specific context of the poem or text in question to verify against, it is not possible to accurately answer the student's query. A recommended next step would be to review the poem "Background, Casually" by Nissim Ezekiel directly for the correct information regarding the protagonist's age when the decision to go abroad is made.