Whatever poet, orator, or sage
May say of it, old age is still old age.
It is the waning, not the crescent moon;
The dusk of evening, not the blaze of noon;
It is not strength, but weakness; not desire,
But its surcease; not the fierce heat of fire,
The burning and consuming element,
But that of ashes and of embers spent,
In which some living sparks we still discern,
Enough to warm, but not enough to burn.

Henry Wadsworth Longfellow (1807–1882) American poet
Poem (1875), “Morituri Salutamus,” l. 262ff
    (Source)

The poem was written for the 50th anniversary of the Bowdoin College class of 1825.

The first two lines here are sometimes (e.g.) misattributed to Sinclair Lewis.