What is the contrast between the liveliness of the swans and human life?

The stark contrast between the liveliness of the swans and human life is that the Swans are still as full of life as they were some nineteen autumns back. The swans still could fly around as much as they want and go wherever they wish to. The poet feels a kind of pain seeing this. He compares himself to the swans and realises the decay n his physical self since he is old now.