S. R. Faruqi:

In this verse the use of ʿumr , which is feminine, with a masculine refrain, according to modern grammar rules is not correct. But the verse is very fine. The one who is passing a lifetime-- that is, a person-- is called a 'traveler'. Here the speaker has called the lifetime a traveler. In the stature's becoming bent, and the 'end of the bridge', a subtle wordplay is that in the bridge too there's a bit of a bend. The traveler passes quickly over the bridge; that is, crossing the bridge takes even less time than crossing a river by boat.

The meaning of the idiom 'end of the bridge' ('promise-breaking' or 'faithless') is so finely linked to the dictionary meaning that it's peerless. In addition, people with whom there is only a commonplace acquaintance, or with whom there would be real, informal friendship but only of a superficial or conventional kind, are called 'end-of-the-bridge friends' [yārān-e sar-e pul]. An allusion to this meaning too is present in the verse.

[See also {923,2}.]

FWP:

SETS == EK; IDIOMS
MOTIFS == ROAD
NAMES
TERMS

The original 'end of the bridge' idea, as SRF once explained it to me, is that since a bridge is narrow it's often crowded, and traffic moves slowly over it (sometimes in only one direction at a time), so that people often have to wait at one end before they can cross; then they often have to wait at the other end for the rest of their party to cross in their turn. They pass the time by striking up conversations, and perhaps even quick friendships, with other travelers in the same situation. Thus this temporary gathering at the 'end of the bridge' becomes an idiomatic evocation of transitory and unreliable acquaintance.

The ik also works enjoyably here-- there's only one lifetime, so is it merely a 'single' or 'particular' one, or is it a remarkable or 'unique' one? And of course, the ultimately friendless and transient 'end of the bridge' traveler is the one who goes off not even with a caravan, but entirely alone, after his fickle lifetime has deserted him.

Any 'natural poetry' fans, take note: this melancholy-looking 'old age' verse comes from the very first of Mir's six divans, and thus was the work of a youthful poet in his twenties. So much for 'autobiography' in the ghazal! Along these lines see also {52,5}.

Compare another use by Mir of the idea of the bent back of old age [{20,6}]:

ham sar-kashī se muddatoñ masjid se bach bach kar chale
ab sijde hī meñ gużre hai qad jo huʾā miḥrāb-sā

[out of {pride / 'high-headedness'}, for a long time we stayed away from the mosque
now our life passes only/emphatically in prostration, since the stature has become like a prayer-niche]

There's also the very different, nostalgically romantic

{584,4}.

For other verses about bent backs, see also-- in the kulliyat-- {27,7}; {680,7}; {697,3}; {1561,2}; {1789,8}. And compare Ghalib's

G{63,4x}.

Note for grammar fans: In the first line, huʾe is best understood as short for huʾe par, a perfect-participial use that would nowadays be replaced by hone par .