Background: Early-onset cholangiocarcinoma (eoCCA) is among early-onset cancers with the fastest rising rates, yet little is known about its biology. We sought to compare the molecular characteristics of eoCCA with average-onset CCA (aoCCA) with an age cut-off of 50 years, utilizing a real-world multi-omics dataset. Methods: The study comprised patients whose tumors underwent molecular analysis at Caris Life Sciences (Phoenix, AZ) using whole exome and whole transcriptome analyses. Patients were categorized by age as eoCCA defined as <50 years and aoCCA >50 years. Gene expression profiles were analyzed for transcriptional signatures predictive of immunotherapy response including the T-cell inflamed score (TIS) and interferon-gamma (IFG) score. P values (adjusted for multiple testing) were considered significant at False Discovery Rate (FDR)P<0.05 for molecular comparisons and FDR P<0.25 for Gene Set Enrichment Analysis (GSEA). Insurance claims data was used for survival comparison using Kaplan-Meier estimates. Results: The study included 5587 patients - 453 patients with eoCCA and 5134 with aoCCA (Table). Of targetable mutations (FGFR2, IDH1, IDH2, ERBB2, BRCA, BRAF), FGFR2 fusion was significantly more prevalent in eoCCA (15.7% vs 5.9% in aoCCA, FDR P<0.001). Rates trended higher in eoCCAfor MSI-H tumors (4.1% vs 2.4%), and high tumor mutational burden (6.1% vs 5.1%) but not significantly different (FDR P=1). The IFG score (Fold Change FC: 1.1, FDR P=0.01) and TIS (FC:17.3, FDR P=0.03) were significantly higher in aoCCA vs eoCCA. On GSEA, angiogenesis was enriched in eoCCA (normalized enrichment score NES=1.51, FDR P=0.16) while IFG (NES= -1.58, FDR P =0.06) and inflammatory response (NES= -1.46, FDR P=0.18) were enriched in aoCCA. Median OS was longer in eoCCA (16.5 vs 13.3 months, Hazard Ratio (HR) 0.86, 95%CI 0.78-0.95, P=0.004). Among patients treated with immunotherapy, median OS was longer in patients with eoCCA (19.2 months, n=19) vs aoCCA (7.6 months, n=150) - HR 0.52, 95%CI 0.28-0.94, p=0.03. No survival difference was identified in patients on chemotherapy (HR 0.91, 95%CI 0.76-1.08, P=0.28). Conclusions: In the largest age-stratified analysis of molecular characteristics of CCA, we identified crucial differences, including higher prevalence of FGFR2 fusions and significant differences in immunotherapy-related markers, angiogenesis enrichment, and inflammatory response. Patients with eoCCA experienced better outcomes with immunotherapy even though immune-oncology-relevant markers favored aoCCA. Our findings, especially higher FGFR2 fusion prevalence in eoCCA, underscore the need for NGS testing and the potential for age-tailored therapeutic strategies.