Final answer:
The correct way to complete the sentence is by using the past perfect continuous tense: 'I had been living in London till the age of five.'
Step-by-step explanation:
The student's sentence 'I_________________ in London till the age of five.' requires the past perfect continuous tense to indicate an ongoing action (living in London) that was completed before another time (age of five). Therefore, the correct completion of the sentence is: 'I had been living in London till the age of five.' This tense is used because it suggests the action of living there took place over a period of time and had been completed by the specified age.
The writings provided are excerpts from various authors depicting different age experiences but don't necessarily guide the grammatical structure needed to complete the sentence in question.