There are large differences across the world in the age at the first marriage for girls. Some regions have experienced a dramatic increase. This can be seen in the new dataset compiled by Gapminder.
Arab women who used to marry very early, now marry later and later. Today a couple is expected to have their own place to live as married. Hence, many families are forced to save for a long time before the young ones are able to marry. This social norm is a relative new phenomenon and is a major explanation for the increased marriage age.
Western Europe have for centuries been characterized by late marriages. Part of the explanation is that the new couple were expected to support themselves from their own farm (or other income source). This also explains why girls in the US married somewhat earlier than in Western Europe: land was more abundant there, and so it was easier to set up your own farm.
About the data
The data is based on a variety of sources, compiled by Gapminder. Definitions may vary between sources. Many countries have a separate source for 2005. We have used average ages, rather than medians. The latter are typically lower than the former. Here you find the documentation for the data.