the hair from behind may serve the purpose of covering a bald spot, and eating a peach may be risky because he has weak, aging teeth or wears dentures. 

The above would seem to indicate Prufrock is an old man.  At the same time, the sense may be present that the speaker is speculating, or envisioning the future.  He may be daydreaming about what he will be like as an old man.  He is daydreaming about mermaids/sirens in the very next line, and is jolted out of his daydream in the final line of the poem by "human voices."  This might indicate Prufrock is not yet an old man.

I told you "Prufrock" was complex. 

In "The Love Song of J. Alfred Prufrock" by T. S. Eliot, we have several pieces of evidence concerning the age of Prufrock. Some are implicit. For example, his caution, primness, concern with propriety, and general self-presentation give him the character of a middle-aged man. As well, though, we have several explicit references to his age.

The most significant passage is:

Time to turn back and descend the stair,
With a bald spot in the middle of my hair—
[They will say: "How his hair is growing thin!"]
My morning coat, my collar mounting firmly to the
     chin,
My necktie rich and modest, but asserted by a
     simple pin—
[They will say: "But how his arms and legs are
     thin!"]

This physical description suggests middle age. Prufrock is not feeble (he descends the stairs unaided) and yet his legs and arms show his age. He is starting to grow bald, but the process is still in progress, and thus again we have a sense of middle rather than old age. His sartorial choices also reflect an upper middle class middle age.

The second passage of relevance is:

  I grow old ... I grow old ...
I shall wear the bottoms of my trousers rolled.

          Shall I part my hair behind? Do I dare to eat a
               peach?
I shall wear white flannel trousers, and walk upon
          the beach.

Again, one sees that Prufrock is growing, but not, yet old, thus suggesting middle age.

J. Alfred Prufrock is not in love with a person in the poem. In fact, the speaker seems quite alone.

One of the hallmarks of Prufrock is that he's not really sure of anything. He wanders around looking for something solid to anchor himself with but is unable to completely do so. Still, he's wandering through the world around him; he keeps moving as he looks for—and doesn't find—connection and meaning.

There is no mention of a specific love interest in the poem. He mentions "you" when he talks about going together, but who that "you" is isn't clear. It could be a love interest, the reader, or a friend, for example. Despite that, Prufrock seems isolated and separate from everyone in the poem. He doesn't speak to anyone. He's too scared to make choices.

There's simply no indication that Prufrock is in love.

In The Love Song of J. Alfred Prufrock by T. S. Eliot, the narrator of the poem is unreliable in an odd way. He is not untrustworthy in the sense of being imperceptive or deceitful or insane; he perceives the world around him clearly and struggles to find truth in it, but he has a major character flaw of indecisiveness. This appears not only with respect to his actions, but also his judgments and interpretations of his perceptions. In other words, although he has certain feelings about the woman, as well as trying to decide whether to reveal his feelings to her, he also has difficulty trying to assess the precise nature of his own emotions. Prufrock himself is not entirely sure whether this is momentary lust, romantic love, or just loneliness and desire for companionship, and thus part of his ambivalence about expressing his feelings is his own uncertainty as to the nature of the feelings. So even Prufrock himself does not really know if he is genuinely in love or not.

Over the course of "The Love Song of J.Alfred Prufrock," Prufrock changes from being a nervous, timid, somewhat ridiculous figure to one who is entirely despairing.

Prufrock begins his description of the visit he is about to make with a series of unenthusiastic images. He knows that he is an unimpressive figure in society, and has never been assertive enough to achieve anything. However, he is also critical of the shallowness of the society he inhabits. His nihilism is all-encompassing.

As the poem progresses, Prufrock's generally negative attitude towards the world becomes focused on himself and his own failures. He ends by admitting that he has not even the stature to be a tragic figure. He is not Prince Hamlet, but merely "an attendant lord," not even the protagonist of his own life. Prufrock concludes the poem with thoughts of his own death, or perhaps merely the continuation of his current living death, which will be obscure and unlamented.

The speaker in T. S. Eliot's "The Love Song of J. Alfred Prufrock" grows old throughout the poem because of his weariness with life and his hesitancy to truly live.

The speaker drifts through his life, moving from one social event to the next, measuring his existence in coffee spoons and focusing his efforts on tea and marmalade. He does not dare to step out of his routine. He is not sure if he should speak to his lady about their relationship. He is not even sure if he can dare to eat a peach. He is so insecure in himself and in his life, and this makes a person grow old quickly.

Further, the speaker is extremely self-conscious. He is concerned about the bald spot on his head and how people will talk about his hair growing thin. He is pulling his coat collar up firmly to his chin like an old man. He thinks about wearing his "white flannel trousers" rolled up and walking along the beach. In fact, he seems about ready to do that now. He is growing old, he says, then repeats the sentiment.

Yes, the speaker is indeed growing old. He is making himself old ahead of his time by his refusal to live his life to the fullest, to take charge of himself, and to reach past the world of social niceties and embrace what it really means to live.