Chronic rhinosinusitis (CRS) is strongly associated with comorbid asthma. This study compares early-onset and late-onset asthma in a CRS population using patient-reported and clinical characteristics. At enrollment into a clinical registry, CRS patients completed the 22-item Sino-Nasal Outcome Test (SNOT-22), Asthma Control Test (ACT), mini-Asthma Quality of Life Questionnaire (miniAQLQ), the 29-item Patient-Reported Outcomes Measurement Information System (PROMIS-29), and medication use questionnaires. Patients also reported comorbid asthma and age at first asthma diagnosis. Early-onset (<18 years) and late-onset (>18 years) asthma groups were defined. Analysis of variance (ANOVA), chi-square, and Kruskal-Wallis tests were used to compare patient responses. A total of 199 non-asthmatic (56.1%), 71 early-onset asthmatic (20.0%), and 85 late-onset asthmatic (23.9%) CRS patients completed the survey. Body mass index (BMI) was significantly higher in late-onset asthmatic (p = 0.046) while age, gender, race, and smoking history did not differ with time of asthma onset. SNOT-22, ACT, and miniAQLQ were not different between asthma groups, but late-onset asthmatics had significantly lower physical function than non-asthmatics (p = 0.008). Compared to non-asthmatics, late-onset asthmatics showed increased rates of nasal polyps (p < 0.001), higher Lund-Mackay scores (p = 0.005), and had received more oral steroid courses (p < 0.001) and endoscopic surgeries (p = 0.008) for CRS management. Late-onset asthmatics compared to early-onset asthmatics showed increased nasal polyposis (p = 0.011) and oral steroid courses for CRS (p = 0.003). While CRS-specific and asthma-specific patient-reported outcome measures (PROMs) were not significantly different among groups, CRS patients with late-onset asthma had poorer physical function, more frequent nasal polyposis, and required increased treatment for CRS. Late-onset asthma may predict more severe disease in CRS.