It is unknown whether the occurrence of ST-elevation myocardial infarction (STEMI) at a younger age is associated with differences in myocardial damage compared with older patients. We aimed to compare the infarct characteristics (area at risk [AAR], myocardial salvage index [MSI], infarct size [IS], microvascular obstruction [MVO]) and clinical outcome in patients aged ≤45 years and >45 years. We analyzed 795 patients with STEMI treated with primary percutaneous coronary intervention. All patients completed 12-month follow-up for the assessment of major adverse cardiac events (MACE). Left ventricular ejection fraction, AAR, MSI, IS, and MVO were determined by cardiac magnetic resonance imaging. Seventy-eight patients (9.8%) were aged 45 years or younger. Young patients were more likely to be male (p = 0.01), to be current smokers (p <0.001), and to have a family history of coronary artery disease (p = 0.05). Contrary, they had significantly lower prevalence of hypertension (p <0.001), diabetes (p <0.01), and 3-vessel disease (p <0.01). There were no significant differences in left ventricular ejection fraction (p = 0.36), AAR (p = 0.30), MSI (p = 0.34), IS (p = 0.29), or MVO (p = 0.58) between both groups. MACE rate was significantly lower in patients aged ≤45 years compared with patients aged >45 years (1.3% vs 7.5%, p = 0.04). After multivariate adjustment for clinical risk factors and cardiac magnetic resonance findings, age remained an independent predictor of MACE (hazard ratio 1.04, 95% CI 1.01 to 1.07, p = 0.03). In conclusion, infarct characteristics are not dependent on age in patients undergoing primary percutaneous coronary intervention for STEMI.