Final answer:
John Keats wrote the majority of his works, including "Ode on a Grecian Urn," between 1819 to 1820, at the age of 24, before he passed away at the age of 25.
Step-by-step explanation:
John Keats was an English Romantic poet who crafted his main body of works over a short period. Keats began his poetic career in 1814, and the bulk of his best-known poems, including the famous "Ode on a Grecian Urn," were written between 1819 and 1820. Given that Keats was born on October 31, 1795, he wrote this particular piece at the age of 24. Sadly, Keats' life was brief; he died at the young age of 25 on February 23, 1821. Keats' lyrical masterpieces were composed at an age that many would still consider the brink of youth, and within these works, he exhibited profound sensitivity to beauty and the human condition.