Aging is a potent risk factor for poor prognosis in subarachnoid hemorrhage (SAH), yet the molecular mechanisms underlying the age-related exacerbation of early brain injury remain incompletely understood. This study investigates the immunometabolic regulation of the microglial senescence-like transition following SAH, focusing on the immune-responsive gene 1 (IRG1)/itaconate axis. We observed that the endogenous upregulation of IRG1 and itaconate is a protective response to hemorrhagic stress that is significantly blunted in aged mice. Microglia-specific IRG1 deficiency exacerbated SAH-induced brain injury, characterized by an accelerated senescence-like transition and the secretion of senescence-associated secretory phenotype (SASP) factors. Mechanistically, we demonstrate that IRG1 deficiency leads to excessive mitochondrial fission and dysfunction via the hyperactivity of Dynamin-related protein 1 (Drp1). Using click chemistry-based proteomics and site-directed mutagenesis, we identified that itaconate exerts its neuroprotective effects by directly alkylating the small GTPase RhoA at the cysteine 107 (C107) residue. This specific post-translational modification inhibits RhoA-GTP binding and downstream ROCK1 activation, thereby suppressing Drp1-mediated mitochondrial fragmentation. Importantly, treatment with the cell-permeable itaconate derivative 4-octyl itaconate (4-OI) rescued mitochondrial dynamics and attenuated microglial senescence and neurological deficits, whereas the RhoA-C107S mutation abolished these protective effects. Collectively, our findings unveil a novel metabolic-mitochondrial checkpoint involving the IRG1/itaconate-RhoA-Drp1 axis. Restoring this pathway represents a promising therapeutic strategy to combat the age-related exacerbation of neuroinflammation and improve outcomes in SAH patients.