Population: age structure (graph) (data July 2013)

Below a graph on how the age groups are divided per country. The top graph shows absolute numbers; the taller the bar how more people it represents. One can deduct from the tallest blue bar for India, that India has more children aged 0-14 than China. One can also see that India has more children aged 0-14 than the USA has people in total!
The bottom graph shows the age groups as a percentage of the countries' total. Here we can see that Nigeria has the youngest population of these ten and that Japan has the oldest.

source: UN, Dept. of Economic and Social Affairs, Population Division (2011). World Population Prospects: The 2010 Revision.
note: projected populations based on the medium-fertility variant.