Got a gut feeling? Well, you may be right!
Human beings have been on planet earth for about 200,000 years. However—a shocking fact—98% of human existence has passed with an average life span of only 19-25 years.  The exponential growth in science and medicine over the last two centuries has increased our life expectancy vastly.
Within the past decade, research focusing on factors that determine aging, longevity, and ability to adapt to environmental influences has been conducted. One factor associated with aging is the microbial composition of our gut. Through this research, scientists will be able to detect your age through only your stool sample. 
Your gut microbiome changes over time
Researchers study bacteria that live in our digestive system, across large groups of people, for various reasons. One reason is to understand the changes in the bacteria over time. These studies include people of various age classes, ethnicities, and different environmental exposures. The results are fascinating. They suggest that, as we age, our gut microbiota evolves and adapts to the requirements of that phase of our life. [1,2]
The research team from the University of Bologna, Italy and their leader Sara Quercia, conducted one of these studies. It focused on changes in the gut microbiota in humans with variables including age, daily life practices, genetic condition and physiology of the person, and dietary shifts. 
For example: During infancy, the gut microbiota is meant to boost the immune system, brain development, and nutritional absorption. But, for a senior, the gut microbiota focuses on enhancing energy intake by breaking down complex sugars. 
We are all born entirely sterile, but within a few hours of birth, microbes start living inside us. This begins the complex relationship between our gut and the tiny beings that will continue to aid us for the rest of our lives. Interestingly, some studies have tried to see if there is any relation between this “pioneer microbiome” across different modes of birth. 
Discoveries showed babies delivered vaginally absorbed microbes from the mother’s birth canal. Those born through cesareans were found to have the same microbes as on the mother’s skin. The first “pioneer microbiome” usually consists of facultative aerobes. But with the intake of breast milk, the gut microbiota changes to obligate anaerobes.
As infancy ends, the gut microbiota slowly starts resembling an adult's. Some argue that a mature adult’s gut microbiota might even attain some stability. However, it is well established that an elderly gut holds more aero-tolerant and pathogenic species. Because there are more of these types of microbes, extra energy is needed to break down sugars into energy for the body. This factor leads to age-related diseases. 
Where you live and what you eat could affect your microbiome
Professor Yatsunenko from the Center for Genome Sciences and Systems Biology at the Washington University School of Medicine conducted an interesting study. They characterized gut microbiota from 531 people living in three different countries.  He along with his co-authors noticed that across these three groups, the way the infant gut microbiota developed remained comparable. But, there were clear differences between the microbiota assemblage of those from the USA and the other two countries. He speculates that the effects of westernization and varied diets could be the reason behind this.
Another group of scientists from the Center for Microbiome Innovation at the University of California, San Diego analyzed over 11,000 stool samples for the American Gut Project.  This study shows that those who eat a larger variety of vegetables have a much more diverse gut microbiota, compared to those who eat fewer and less variety of vegetables. This is in comparison to those who eat fewer and less varied vegetables. Also, eating different vegetables seems to help us metabolize food in more than one way.
Is there a link between aging and the gut microbiome?
Looking back at these studies, we can see scientists often tend to pose a question which might be slightly difficult to answer. While it is true that gut microbiota can reveal your age, could it also be true that your aging process is governed why what's in your gut? Researchers have linked poor gut microbiota to depression, behavioral changes, pronounced physiological stress, and increased risk of diseases. [4,6] Therefore, it is vital that one takes care of the microbes living in their digestive system and make sure to always listen to our gut. Order your Gut Intelligence Test kit today from Viome to find out which foods you personally need for a healthy microbiome.
Related Article: What Your Poop Says About You
Valle Gottlieb, M.G., Closs, V.E., Junges, V.M. and Schwanke, C.H.A., 2018. Impact of human ageing and modern lifestyle on gut microbiota. Critical Reviews in Food Science and Nutrition, 58(9), pp.1557-1564.
O’Toole, P.W. and Jeffery, I.B., 2015. Gut microbiota and ageing. Science, 350(6265), pp.1214-1215.
Quercia, S., Candela, M., Giuliani, C., Turroni, S., Luiselli, D., Rampelli, S., Brigidi, P., Franceschi, C., Bacalini, M.G., Garagnani, P. and Pirazzini, C., 2014. From lifetime to evolution: timescales of human gut microbiota adaptation. Frontiers in microbiology, 5, p.587.
Galkin, F., Aliper, A., Putin, E., Kuznetsov, I., Gladyshev, V.N. and Zhavoronkov, A., 2018. Human microbiome ageing clocks based on deep learning and tandem of permutation feature importance and accumulated local effects. bioRxiv, p.507780.
Yatsunenko, T., Rey, F.E., Manary, M.J., Trehan, I., Dominguez-Bello, M.G., Contreras, M., Magris, M., Hidalgo, G., Baldassano, R.N., Anokhin, A.P. and Heath, A.C., 2012. Human gut microbiome viewed across age and geography. nature, 486(7402), p.222.
McDonald, D., Hyde, E., Debelius, J.W., Morton, J.T., Gonzalez, A., Ackermann, G., Aksenov, A.A., Behsaz, B., Brennan, C., Chen, Y. and Goldasich, L.D., 2018. American gut: an open platform for citizen science microbiome research. systems, 3(3), pp.e00031-18.