This study presents a lifespan multi-tissue proteomic atlas of non-canonical peptides in C57BL/6 mice. Brown adipose tissue, cerebral cortex, liver, lymph nodes, and serum were analyzed at 1, 6, 12, 18, and 24 months of age using data-independent acquisition mass spectrometry (DIA-MS). An expanded protein sequence database integrating canonical mouse proteins with open reading frames derived from intronic regions, non-coding RNAs, gene fusion-related sequences, and mouse-associated microbial proteins was used for peptide identification. A total of 985 non-canonical peptides were detected, showing pronounced tissue specificity and distinct age-associated expression patterns. The study characterizes organ- and life-stage-specific remodeling of the non-canonical proteome across mouse development, maturation, and aging, and provides an age-resolved resource for investigating non-canonical translation products beyond conventional protein annotations.