Closely following, in Sonnet CIV., the poet says:

To me, fair friend, you never can be old,
For as you were when first your eye I eyed,
Such seems your beauty still. Three winters cold,[[10]]
. . . . .
In process of the seasons have I seen,
. . . . .
Since first I saw you fresh, which yet are green.
Ah! yet doth beauty, like a dial-hand,
Steal from his figure, and no pace perceived;
So your sweet hue, which methinks still doth stand,
Hath motion, and mine eye may be deceived[[11]]:
For fear of which, hear this, thou age unbred;
Ere you were born was beauty's summer dead.

The thought is: your beauty may be passing; it may be that my eye that sees it not, is deceived. We should carefully note the words, "Three winters cold," "Since first I saw you fresh, which yet are green." Though they present no clear or sharp indication as to the age of his friend, yet I think that of them this may be fairly said: the word "green" is used as opposed to ripe or matured, and his friend's age is such that three years seem to the poet to have carried him a step toward maturity. And so reading these words, they harmonize with the expression of the poet's fear that his great love for his friend may have prevented him from seeing his beauty

like a dial hand,
Steal from his figure.

In Sonnet LXX. the poet says of his friend:

And thou present'st a pure unstained prime.
Thou hast pass'd by the ambush of young days,
Either not assail'd, or victor being charged.

In Sonnet LXXVII. the poet says:

The wrinkles which thy glass will truly show
Of mouthed graves will give thee memory;
Thou by thy dial's shady stealth mayst know
Time's thievish progress to eternity.

Sonnet CXXVI. is as follows:

O thou, my lovely boy, who in thy power
Dost hold Time's fickle glass, his sickle, hour;
Who hast by waning grown, and therein show'st
Thy lovers withering as thy sweet self grow'st;
If Nature, sovereign mistress over wrack,
As thou goest onwards, still will pluck thee back,
She keeps thee to this purpose, that her skill
May time disgrace and wretched minutes kill.
Yet fear her, O thou minion of her pleasure!
She may detain, but not still keep, her treasure:
Her audit, though delay'd, answer'd must be,
And her quietus is to render thee.