«My glass shall not persuade me I am old,
So long as youth and thou are of one date».
Until now, the poet’s feelings have soared to the level of rapture; in Sonnet 22, he suggests — perhaps deluding himself — that his affections are being returned by the youth. He declares that the youth’s beauty “Is but the seemly raiment of my heart, / Which in thy breast doth live, as thine in me.”
My glass shall not persuade me I am old,
To reconcile himself to his physical decline caused by aging, the poet argues that so long as he holds the youth’s affection, he and the youth are one and the same; he can defy time and his own mortality because he measures his physical decline by how the young man ages. So long as the youth remains young, so will the poet.
The image of the poet and the youth exchanging hearts is expressed in highly intimate language: The poet assures the youth that he will keep the youth’s heart “As tender nurse her babe from faring ill.” Such language assumes an exchange of affection, but it also reveals the problem of an older lover trying to dismiss the age difference between himself and his much younger lover. By the sonnet’s end, the poet appears overly possessive of the youth: “Presume not on thy heart when mine is slain; / Thou gav’st me thine not to give back again.”
English audio from YouTube Channel Socratica
Summary from Cliffsnotes.com