لَيْتَ الشَّبَابَ يَعُودُ
Would that youth returned.
Layta behaves grammatically like inna: al-shabāba is its accusative subject, while the verbal clause yaʿūdu functions as its predicate. Its rhetorical force is a wish, not an assertion.
Comparative review
ParticleTypical rhetorical use
ليتPrimary marker of wishing
هلInterrogation used as a wish
لوConditional form used for wishing
هلّاExhortation or past reproach
لولاExhortation or reproach