Duchenne muscular dystrophy (DMD) is a severe and progressive muscle wasting disease characterized by chronic inflammation, poor myogenesis, and replacement of muscle tissue with extracellular matrix. Lack of dystrophin forms the genetic basis of DMD, however, disease severity may vary greatly between patients based on specific genetic modifiers. The D2-mdx mouse is a model for severe DMD pathologies that exhibits exacerbated muscle degeneration and failure to regenerate in response to spontaneous or acute injuries, even in the juvenile stage of the disease. We show that poor regeneration of juvenile D2-mdx muscles is associated with an enhanced inflammatory response to muscle damage that fails to resolve efficiently and supports excessive accumulation of fibroadipogenic progenitors (FAPs) and extracellular matrix. Unexpectedly, the extent of damage and degeneration observed in juvenile D2-mdx muscles is markedly reduced in adults, and further, is associated with the restoration of the inflammatory and FAP responses to muscle injury. These improvements enhance myogenesis in the adult D2-mdx muscle, reaching levels comparable to the milder (B10-mdx) mouse model of DMD. Ex vivo co-culture of healthy satellite cells (SCs) with juvenile D2-mdx FAPs reduced their fusion capacity as compared to co-culture with FAPs from acutely injured healthy muscle. Our findings indicate that aberrant stromal cell response contributes to poor myogenesis and greater muscle degeneration in severely dystrophic juvenile D2-mdx muscles, while reversal of this response lessens pathology and improves mitogenicity in adult mouse muscle. This work supports use of the D2-mdx to investigate the mechanisms that contribute to the onset of severe DMD pathologies and identifies the cross-talk between immune and stromal cells as a therapeutic avenue to treat severely dystrophic DMD muscles.