The average age (mean not median) is about 32 years in 2016 and is increasing by about 1 month every year ( about 1 year per decade). It will be almost 42 years by 2100.
graphic by The Economist
The median age (50% of population greater than this age) is 30.1 years in 2016 (male: 29.4 years,
female: 30.9 years). The median age is growing just a little faster than the average age as global fertility declines and will be about 37 by 2050.
graphic by Pew Research
The k2p blog 