The correct answer is metaphor. A metaphor is a rhetorical figure of speech where two or more things are symbolically compared, without using the words such as like or as (because that would be a simile). This whole poem is symbolical/metaphorical - it talks about the passage of time and how everything is transient and fleeting.
It's metaphor, since "Her early leaf's a flower" saying one thing is another without using the word 'like'. A simile does a similar thing, but it does use the word 'like'. An onomatopoeia is a word that sounds like a sound, and personification is giving a nonhuman thing human attributes.
