Although it seems that your gut microbes (which are completely capable of regenerating themselves) will never age, this is unfortunately not the case. In the same way that a 30-person knee does not crawl like those in a centenary, the intestinal gland changes with age. , they found that adults had a loss of overall healthy microbes and an increase in inflammatory microbes. The genetic makeup of the older microbiome is less capable of processing fiber and producing short-chain fatty acids (SCFA). As you know, SCFAs are the currency of gut health and critical to whole-body health. So don't be less capable of making them a sign of diminished health or, in other words, aging.
In a separate study outside Ireland, researchers have shown that aging is associated with a decrease in gut diversity. Diversity is important to gut health, and when we lose variety, we tend to put ourselves at risk for disease. And once again, they see the loss of germs that produce SCFAs.
Collectively, it appears that gut microbes are, in fact, declining with age and that these changes may help to explain the occurrence of disease that occurs as we age. For example, a 2017 study found that brain amyloid, the substance that causes Alzheimer's disease, is associated with an increase in the level of pro-inflammatory microbes in cognitively impaired adults.