The UN definition of an adult is an individual over the age of 15. In 1900, adults were 1.1 billion out of 1.6 billion total people (so there were more over-15s than under-15s). Today there are 7.5 billion total people, of whom 5.5 billion are adults (leaving 2 billion children).
By 2050, there will likely be 7.6 billion adults in the midst of 9.7 billion people, or roughly the same ratio.Some places have higher birth rates and therefore younger (on average) populations. In others - and particularly in some unevangelized regions - declining birth rates means the population is ‘aging’.
In the table below, we look at the situation in a slightly different fashion: the total population under the age of 15, versus the total population over 65; or, children vs. seniors. The final column shows the ratio between these two populations, presented as children divided by seniors. In low-income countries, for example, children under the age of 15 outnumber seniors six times over.
This kind of ratio suggests how ministry resources might be strategically allocated. In low-income countries, obviously more resources should be devoted to ministry to children than to ministry to seniors, in the sense that there are more children to minister to. But in many countries, the division is nearly equal. People are living longer, and having fewer children.
We must become just as good at ministering to the elderly (especially in places where the ratio is under 1.0) as we are at ministering to children. Unfortunately, anecdotally it appears to me there are far more short-term trips to minister to children than to senior citizens.