You might find it helpful, when considering this question, to ask yourself the following question: Does a life that is measured out by "coffee spoons" seem to be a life that has been exciting and heroic or boring? Think of all the things that we could use to measure our lives: our achievements, places we have gone to, things we have done, people we have known, legacies we have left behind us. J. Alfred Prufrock, however, can only look upon his life as a life that has been characterised by innaction, passivity and meaningless interactions that have not amounted to anything. Note the context of the quote you have given:
For I have known them all already, known them all--
Have known the evenings, mornings, afternoons,
I have measured out my life with coffee spoons;
I know the voices dying with a dying fall
Beneath the music from a farther room.
So how should I presume?
Note the world-weary and bored tone of the speaker in this stanza. His life seems to have been marked by nothing more exciting than a series of meaningless interactions with others over coffee or tea. A life that can only be measured out by coffee spoons suggests a life of a cautious, fearful person, a life of someone who is afraid of adventure, excitement, danger and risk. This is of course an excellent description of the life of J. Alfred Prufrock with his narcissistic, self-absorbed fears that dominate so much of the poem.