What do you think elderly actually means?
From a purely prescriptive perspective, it means old. Which is fine and dandy when using the adjective in a wholly objective manner. Gets used a lot in medical/scientific literature in that fashion.
From a descriptive linguistics perspective it functions to flesh out a picture.
What the fleshing out intends to convey depends on the user and is coloured by factors like their culture, perspective and motivation. It is not necessarily a neutral, objective observation.
The intent behind its inclusion is not always devoid of bias, or without agenda. "An elderly grandmother" was used relentlessly by the alt-right to undermine the perception that Hillary was strong enough and well enough to take on a presidential role.
Going back to the example on this thread, "An elderly woman, 74" might reflect that a reporter had been informed (but as yet not allowed to report) that the missing woman was suffering from frailties we associate with advanced years.
Depending on the circs of how she went overboard, it might be setting up an image to underline how defenceless she was, if she was pushed for example. Or prepping an intended story line to explain a suicide. Or creating a hypothetical basis for an accident. Or to underline just how mysterious her going overboard was, cos her being able to climb over barriers like a spritely mountain goat was a long shot.
On the other hand, it might just reflect that the reporter is a fairly young snotbag, who thinks everybody over 50 is pretty much past it, and is subconsciously thinking "let's not get too excited about this particular case cos she had one and half feet in the grave already".
It is also possible there was a minimum word count for the report. There was little info to be had, so it functioned as padding and "old" felt too blunt.
Words mean not just what they mean in a purely prescriptive sense. How we use them, why we use them, brings layer upon layer of communication on top.
And it is bloody fascinating.