measured out my life with coffee spoons
that's something typical of English. so even if you ARE mature, you won't measure it out with coffee spoons cuz...you're not English. In the same reasoning, even if you are immature, you could still measure it out with coffee spoons since that'd be your lifestyle. This is simply an allusion to Macbeth, I don't think that you quote it that appropriately. I'd suggest another passage.
btw, how old do you think prufrock is? he's actually only 35-45 range.
not from the grand and magnificent
well the quote itself isn't grand. the entire story focuses on whether Prufrock'll ask that girl out. THAT'S IT!!! It's nothing great, if not for the hidden theme: To be or not to be. He's chosen to not be, a cowardly act. What would you choose?
overall, I think that you've got the style, but not the poem entirely. It's not as much about maturity and really making an impact on the world as simply facing moments of doubt, which could be as small as asking a girl out, and you've got to avoid Prufrock's cowardice and choose to be, to follow your heart and not care about what others speak of you.