The Old World
It's not your grandmother's Germany anymore. Though if you live in Germany, you probably are a grandmother - or would be if your children had ever gotten around to reproduction. The median age in Germany is 46.1 years, an age at which many people used to be grandparents. It's tied by Japan in that regard, and only exceeded by the comic opera state of Monaco, with a median age of 51.1. The 43 countries in the over 40 category are mostly in Europe and mostly the long industrialized countries.
The slightly less superannuated countries in the 35-40 median age category include most of the rest of Europe and advanced nations: the US (37.6), China (36.7), Australia (38.3), to name a few.
The middle-aged 30-35 category includes a few tiny Muslim enclaves in Europe, Brazil, and a sprinkling of nations from all over.
The 25-30 category includes India (27.0), Mexico (27.3), Iran (28.3), and Israel (29.9), as well as other big chunks of Latin America and Asia, North Africa, and South Africa.
Under 25 is the realm of the not quite yet developed: Bangladesh (24.2), Philippines (23.5), Laos (22.2), Ghana (20.8) and under 20 is mostly basket case countries: Yemen (18.6), South Sudan (16.8), Niger (15.1).
The world's median age is 29.4. It's surprising how much this one statistic captures about countries.
I like numbers, OK?