This is my favourite CwP picture in a long time! Some extra context is always fun, I'm not sure if you'd checked, but this amazing machine is what it's from!
I hate to say it, but this one is entirely inaccurate. 19103 is the post code for western Center City Philadelphia (I was actually there on Saturday for an event). It is an extremely dense area, but most of it is likely rented out to younger individuals. This would make sense if the statistics were for home ownership or something along those lines, but in terms of the actual demographics, the average age is much lower.
The statistic is for noninstitutionalized sensory-disabled residents. If it is a dense area, even if most of it's rented out to young people, could there not still be 600 elderly somewhere there? It certainly makes sense that less young people would be sensory-disabled. The weird thing about City-Data tends to be the way they present the data, whether the data is accurate or not—this applies here too, as one might wonder why one of the age groups is so much smaller than the others.
...And this, folks, is why you read your sources. I automatically assumed this was a general population graph My bad! I find the existence of this shirt particularly intriguing, because 19109 is apparently only the land area of one block, with a skyscraper, a bowling alley, and a handful of businesses. I can understand someone being prideful of their zip code or area code (here in Delaware, a local way to distinguish a local versus someone from out-of-state is whether they say our area code as "three oh two" or "three zero two"), but there is barely anyone living here for them to be prideful about it. Even in the densest areas, it's fairly rare to have post codes that are so small, unless they are used exclusively for PO Boxes (usually those with a 9 as the fourth digit; Philly has 19092, 19093, 19099, 19190-19197, and my hometown of Wilmington DE has 19890-19899).
Hm, interesting. They might be auto-generated. At the very least here's another. It's slightly different, though!