a person no longer young and thinking about life
In the poem the sunflower watches the sun travel across the sky. It says that it "countest the steps of the sun". Then mentions "the traveller's journey is done". It shows the passage of time and the aging of the speaker who is now looking back on life.
Options A and E are completely wrong and can be eliminated immediately. Option C, while describing the natural world, does not use the sunflower to symbolize it. We also do not see evidence of Option B, a search for enlightenment.