This paper presents a conceptual re-examination of the age of the universe based on a light-centered interpretation of causality and time.Rather than treating time as a pre-existing background parameter, this work adopts the standpoint that time emerges only when the speed of light becomes well-defined, and causal structure is established. From this perspective, the cosmic microwave background (CMB) is interpreted not merely as residual radiation from an early hot phase, but as a fundamental observational trace of the moment when light propagation became fixed and time itself first manifested.Consequently, the age of the universe is discussed as a quantity derived from light-based causal structure, rather than from conventional spacetime expansion alone. This approach is designed to remain mathematically minimal while emphasizing conceptual consistency with redshift phenomena discussed in a related companion paper.The results suggest that revisiting cosmological age estimation through the primacy of light and causality may offer an alternative framework for understanding the origin and evolution of the universe.
Akihito Sugawara (Sat,) studied this question.