This 2023 rodent study investigated aging processes and gut microbiota in crowded conditions:

“Our study provides clear evidence that high-density crowding accelerates the aging process of Brandt’s voles. We also found that ‘high-density microbiota’ promote the aging-related phenotype in voles.

Because we minimized effects of direct fighting on mortality of voles, observed changes in lifespan in this study should mostly represent the natural aging processes of voles.

High density increased the level of stress hormone corticosterone, which disrupted gut microbiota composition by:

• Decreasing abundance of anti-aging or anti-inflammatory bacterial species; and
• Increasing the proportion of pathogenic bacteria.

This caused an increase in DNA oxidation and inflammation through upregulation of NF-kB and COX-2 pathways.

Although high-density relief and butyric acid administration interventions could reverse aging-related processes of adult voles, it remains unclear whether they could reverse the aging process in terms of lifespan.

Our results suggest that gut microbiota play a significant role in mediating aging-related processes of voles under high-density conditions, and can be used as a potential therapeutic target for treating stress-related diseases in humans.”

https://onlinelibrary.wiley.com/doi/10.1002/advs.202205346 “Gut Microbiota is Associated with Aging-Related Processes of a Small Mammal Species under High-Density Crowding Stress”

I came across this study by it citing Reversing hair greying for effects of stress interventions.