Analysis of 8,115 fecal samples across five continents reveals a dramatic gut microbiome phase transition occurring between ages 56-60, marking a critical inflection point where microbial communities lose ecological stability and core species abundances shift substantially. Seven key species, including Escherichia coli, show phylogenetic divergence with enhanced cell motility, altered carbohydrate metabolism, and increased horizontal gene transfer in older individuals. The research demonstrates that disease associations with gut microbiota age change significantly before and after this 56-60 year threshold. This finding represents a paradigm shift in understanding microbial aging, suggesting the gut microbiome doesn't decline gradually but undergoes an abrupt transition resembling other biological phase changes like menopause. The timing aligns remarkably with when many age-related diseases accelerate, potentially explaining why certain health interventions show variable effectiveness across age groups. The discovery opens therapeutic windows for microbiota-based interventions specifically targeting this transition period. However, the observational nature means causality remains unclear—whether microbiome changes drive disease risk or vice versa. The global dataset strengthens generalizability, but individual variation around this transition point likely exists.