"Sonnet 19" by William Shakespeare is a sonnet that deals with Time's power over human beings. No matter what we want and do in life, no matter our goals, dreams, and initiatives, they are all at the mercy of Time. Time rolls on and we have no say in the matter. Time ravages people, places, animals, and things. The steady, unrelenting movement of Time also plays with the mind of people, as they seek to achieve - knowing they will not live forever in this physical life here on earth.
The speaker in the sonnet recognizes that time has power over even the "powerful". As Post #1 states, Time has power over strong wild animals such as tigers and lions. The poet, in essence, is pleading with time to do whatever it will, but to refrain from making his beloved grow old. He does not want her physical body to experience the ravages of time - becoming wrinkled and such. He wants Time to stop its assault on his beloved, evidenced in the line...
Nor draw no lines there with thine antique pen;
In the end, the sonnet conveys the message that no matter what Time does, the poet has immortalized his beloved's youthful beauty in this sonnet. With the words of this sonnet she will be preserved as forever young.