The age at onset of myasthenia gravis (MG) represents a crucial determinant in understanding its pathophysiology, clinical presentation, and therapeutic response. Age influences the immunological profile and thymic pathology and affects disease severity and treatment outcomes. This chapter delves into the clinical and scientific nuances distinguishing early onset MG (EOMG), late-onset MG (LOMG), and very late-onset MG (VLOMG), underscoring the role of age in shaping disease trajectories and management strategies.

The stratification of MG into EOMG, LOMG, and VLOMG is based on specific age cut-offs, which reflect distinct clinical and immunological characteristics. Historically, the threshold proposed to distinguish between early and late-onset MG was set at 40 years. However, accumulating evidence highlighted specific differences in disease mechanisms and clinical features between individuals with onset below and above 50 years of age. This led to adopting 50 years as the cutoff age for EOMG and LOMG (Aarli, 1999, Bhandage et al., 2024). The concept of VLOMG, characterized by disease onset at 65 years or older, has gained attention in recent years due to improved diagnostic capabilities and the increasing proportion of aging populations globally (Bi et al., 2023, Braun, 2024, Carr et al., 2010).