Wordsworth in "The Rainbow" sees his life as existing in 3 stages. What are these three stages?

William Wordsworth was a Nature poet who worshipped Nature as his God. For Wordsworth, Nature was his main source of spirtual comfort  and escape from all the cares of this world. His association with life giving and life sustaining Nature began even when he was only a child and remained with him till his death.

In this short lyric, the 'rainbow' symbolizes the life sustaining and life nourishing goodness of Nature. The sight of the beautiful rainbow which he saw when he was only a child is deeply etched in his memory and the same joy that he experienced when he saw it as a child contiunes to remain with him through his adulthood. He desires that this same childhoood joy should continue to sustain him even in his old age. Wordsworth says that he would rather die than not being able to experience the same joy that he experienced when he saw the rainbow when he was a small boy after he becomes an old man.

The memory of the beautiful rainbow and its pleasant associations form the link between his childhood, adulthood and his old age:past, present and future. Wordsworth concludes the poem by expressing the desire that each day of his existence be linked with the next by beautiful and simple natural sights like the rainbow.

The rainbow which he saw when he was a child becomes the 'objective correlative' in the literary text which recalls to his mind the pleasant memories associated  with the beautiful rainbow.