Demographics and Wealth in MENA

In response to Friday's overview of the Middle East and North African (MENA) countries,  a reader writes to say:

You omitted one key factor: the percentage of the population in the young adult 18 to 25 year range. There are very few solid facts, or repeatable observations, in sociology; one of the few I have found is that social stability is at risk when you have a significant percentage (circa 20%) of the population in the 18-25 range. Remember Paris in '68? Haight- Ashbury? Those were boom times. Add in scarce jobs, high inflation, and poor future prospects, well then you have an explosive cocktail.

That seems right to me also.  To explore the issue, I found country level data at the UN for median age and (manually!) transcribed it to a spreadsheet with the IMFs estimates of 2009 GDP/capita (at PPP).  Here are the data, with the MENA countries in red.

As you can see, generally, wealthy countries are older: poor countries tend to have both higher birth rates and low life expectancy, which skew the age distribution toward the young.  You can also see the MENA countries almost all lie on the low side of the trend (relatively young populations for their wealth level).

If we look instead at OPEC countries versus MENA countries, you can see that these are even more so:

I imagine the basic reason is the resource curse: these country's wealth tends to go into the hands of a small extremely wealthy super-elite, and the rest of the country is like a much poorer country than the GDP/capita suggests.

I have circled Saudi Arabia, which seems particularly far from the trend.