Which of the following is more commonly associated with a nonmalignant form of monoclonal gammopathy (MGUS)?

The association of being over the age of 60 at the time of monoclonal protein discovery with nonmalignant monoclonal gammopathy (MGUS) is grounded in the epidemiological understanding of this condition. MGUS commonly occurs in older adults, and the prevalence increases with age. While MGUS itself is a benign condition characterized by the presence of a monoclonal protein in the serum, it serves as a precursor to more serious conditions, such as multiple myeloma, but often requires no treatment.

The other choices pertain to different aspects of monoclonal gammopathy. The percentage of plasma cells in the bone marrow and the type or concentration of the M-protein can vary significantly in MGUS and may not distinctly indicate a benign condition. Although finding an IgG type of M-protein and higher concentrations can occur in MGUS, they are not definitive markers for distinguishing it from malignant forms of gammopathy. Hence, being over 60 years old is an important demographic factor that correlates with the occurrence of MGUS in the general population.