elderly gentleman; old gentleman
A polite, somewhat formal term for an older man of refined or gentlemanly bearing. Often used in literary or respectful contexts.
An elderly gentleman was sitting quietly on a bench in the park.
The old gentleman was very courteous.
お年寄り is a general, polite term for an elderly person, without the 'gentlemanly' connotation of 老紳士.
Compound of 老 (rou, 'old') and 紳士 (shinshi, 'gentleman'). The exact historical derivation is uncertain, but the word follows standard Sino-Japanese compounding patterns.