What does the speaker want when he grows old

In Lines 3-5 of "My Heart Leaps Up" William Wordsworth sees his life in three parts, as a young child ("when my life began"), as a man ("So is now I am a man) and as an old man " (So be it when I shall grow old"). As he says in the poem, he hopes he will always see nature as something beautiful and can retain that mystical wonder when his "heart leaps up" when he sees a rainbow, or something beautiful in a natural setting.