Previous studies in adults admitted to pediatric hospitals primarily investigated associations between complex chronic condition characteristics and patient outcomes. Our study explored the association of age with length of stay (LOS) and total cost in these adults, accounting for other patient factors. Using the Pediatric Health Information System, we included 1,215,736 patient encounters from 2021 to 2022. Unadjusted and adjusted analyses were performed using bivariable and multivariable log-linear regression. There was a significant positive association between age and total cost, with adults 18-20 years having 13% higher total cost (95% confidence interval [CI]: 12%-15%), 21-25 years with 25% higher total cost (95% CI: 22%-29%), and 25-99 years having 72% higher total cost (95% CI: 66%-79%) than 1-17 years. Our findings suggest expanding upon the existing status quo to identify the most appropriate environment to care for this unique and growing population, especially given the anticipated reduction in pediatric beds and subspecialty expertise.