Many young aspiring writers expect too much of themselves. Typically they graduate from college at around the age of twenty-two. They consider themselves "educated" and ready to start earning their livings as professional freelance writers. Graduating from college is just morphing from being a senior in one college to becoming an entering freshman at a higher college called The School of Hard Knocks. Milton lived centuries ago, but he was not too much different in his aspirations and expectations from many young aspiring writers of today. Here he was at the grand old age of twenty-three. Why wasn't he producing masterpieces? For one thing, he hadn't acquired much worldly experience. His mind was saturated with reading in many different languages. He really needed ten years of maturation and worldly experience before he would have something to say.
Here is a pertinent quote from a twentieth-century motion picture about an aspiring young writer:
A writer. Silly, isn't it? You know, in college I passed for a genius. They couldn't get out the college magazine without one of my stories. Boy, was I hot, Hemingway stuff. I reached my peak when I was nineteen. Sold a piece to the Atlantic Monthly. Reprinted in the Readers' Digest. Who wants to stay in college when he's Hemingway? My mother bought me a brand new typewriter, and I moved right in on New York. Well, the first thing I wrote, that didn't quite come off. And the second, I dropped. The public wasn't ready for that one. I started a third and a fourth...only by then, somebody began to look over my shoulder and whisper, in a thin, clear voice like the E-string on a violin. Don Birnam, he'd whisper, it's not good enough. Not that way. How about a couple of drinks just to set it on its feet, huh? So I had a couple. Oh, what a great idea that was. That made all the difference. Suddenly I could see the whole thing...the tragic sweep of the great novel, beautifully proportioned. But before I could really grab it and throw it down on paper, the drinks would wear off and everything would be gone, like a mirage. Then there was despair, and a drink to counterbalance despair, and one to counterbalance the counterbalance. And I'd sit in front of that typewriter, trying to squeeze out one page that was halfway decent, and that guy would pop up again.
From screenplay of The Lost Weekend (1945), based on the novel by Charles R. Jackson
Well, you are sixteen years old, or something like that, right? Don't feel bad for not getting it. The poem was written by a young man who was a good seven years older than you are now. Thus fret not about the fact that Milton's Sonnet 7 "ON HIS BEING ARRIVED AT THE AGE OF 23" is a bit tough for you to understand.
Generally, the theme of the poem deals with age and aging. The narrator (you wouldn't be wrong if you figured it was Milton himself on or near his twenty-third birthday) is talking about being and acting his age. In the first eight lines, he says something like: My, how time flies, and here I am twenty-three already. How did that happen so fast. And, although I may not look my age:
Perhaps my semblance might deceive the truth,
That I to manhood am arrived so near,
nonetheles, here I am almost a man.
The last six lines are a reassurance. He realizes that whether or not he looks it, or is quite ready, he will soon enough blossom into the man and poet he has so diligently prepared himself to be.