Depending on sex, genetic and environmental factors, shrinkage of stature may begin in middle age in some individuals but tends to be universal in the extremely aged. This decrease in height is due to such factors as decreased height of inter-vertebral discs because of desiccation, atrophy of soft tissues, and postural changes secondary to degenerative disease. Working on data of Indonesia, the study by Baten, Stegl and van der Eng suggests a positive relationship of economic development and average height. In Indonesia, human height has decreased coincidentally with natural or political shocks. Average height around the world
As with any statistical data, the accuracy of such data may be questionable for various reasons:

Some studies may allow subjects to self-report values. Generally speaking, self-reported height tends to be taller than its measured height, although the overestimation of height depends on the reporting subjects height, age, gender and region. Test subjects may have been invited instead of chosen randomly, resulting in sampling bias. Some countries may have significant height gaps between different regions. For instance, one survey shows there is 10.8 cm (4+1⁄2 in) gap between the tallest state and the shortest state in Germany. Under such circumstances, the mean height may not represent the total population unless sample subjects are appropriately taken from all regions with using weighted average of the different regional groups. Different social groups can show different mean height.
"Mean Body Weight, Height, and Body Mass Index, United States 1960–2002" (PDF). Advance Data from Vital and Health Statistics (347): 1–17. PMID 15544194. "Health Survey for England – trend data". Department of Health and Social Care. Archived from the original on 10 October 2004. Bilger, Burkhard (29 March 2004). "The Height Gap". The New Yorker. Archived from the original on 2 April 2004. A collection of data on human height, referred to here as "karube" but originally collected from other sources, is archived here. A copy is available here (an English translation of this Japanese page would make it easier to evaluate the quality of the data...)
"Americans Slightly Taller, Much Heavier Than Four Decades Ago". National Center for Health Statistics. 27 October 2004. Aminorroaya, A.; Amini, M.; Naghdi, H. & Zadeh, A. H. (2003). "Growth charts of heights and weights of male children and adolescents of Isfahan, Iran" (PDF). Journal of Health, Population, and Nutrition. 21 (4): 341–346. PMID 15038589. S2CID 21907084. Archived from the original (PDF) on 19 September 2018. 6. Celostátní antropologický výzkum dětí a mládeže 2001, Česká republika [6th Nationwide anthropological research of children and youth 2001, Czech Republic] (in Czech). Prague: State Health Institute (SZÚ). 2005. ISBN 978-8-07071-251-1. Bogin, Barry (2001). The Growth of Humanity. Hoboken, NJ: Wiley-Liss. ISBN 978-0-471-35448-2. Eveleth, P.B. ; Tanner, J.M. (1990). Worldwide Variation in Human Growth (2nd ed.). Cambridge University Press. ISBN 978-0-521-35916-0. Miura, K.; Nakagawa, H. & Greenland, P. (2002). "Invited commentary: Height-cardiovascular disease relation: where to go from here?". American Journal of Epidemiology.