Coleridge's speaker laments the losses that come with age as the poem begins:

"Verse, a breeze mid blossoms straying, 

Where Hope clung feeding, like a bee— 

Both were mine!"

Themes of Romanticism can be found in Coleridge's poem.  The emphasis on the natural world is a critical element in the poem and something found in many of the poem's lines.  The opening lines in the poem are akin to an invocation of the natural world:  "Verse, a breeze 'mid blossoms straying,/ Where Hope clung feeding, like a bee."  "Friendship is a sheltering tree" or "Love is flower- like" and "tears take sunshine from thine eyes" are all examples of the presence of nature in the poem.  Romantic thinkers like Coleridge emphasized a strong link between consciousness and the experience of the natural world and Coleridge underscores this connection in the poem.

Additionally, I think that the Romantic theme of subjective emotions being used to construct reality is present in the poem.  Romantics believed that the subjective emotional experience was the only acceptable frame of reference to understand reality.  They wanted to inject emotions and feelings into as many domains as possible.  The subjective experience on what it means to be young is a part of Coleridge's poem.  He wishes to explore the joy in being young and revel in it from an emotional point of view.  The hopeful view of youth and the reveling of it from a subjective frame of reference are elements that capture the theme of personal experience that is so much a part of the poem and Romanticism, as a movement.