Ulcerative colitis (UC) differs between patients first presenting as children or as adults. A new longitudinal study in the Inflammatory Bowel Diseases journal explored the microbiota profile of patients with pediatric and adult-onset UC. The study found reduced microbial diversity and stability in pediatric patients and detected bacterial species that associate differently with disease activity across the two groups. These findings raise some interesting questions about whether we should consider age of onset when it comes to microbiome studies, including, and importantly, microbiome-based interventions.