Donor age is one factor to optimize allogeneic hematopoietic cell transplantation (alloHCT). Therefore, we investigated whether young unrelated donors (UD) provide a benefit for older patients with myeloid malignancies compared to HLA-identical sibling donors (MSD). We performed a retrospective registry study on patients ≥50 years who received a first alloHCT between 2010 and 2020. We compared event-free survival (EFS) of patients who were transplanted from MSD aged ≥50 years versus UD aged ≤35 years who were HLA-compatible for HLA-A, -B, -C, and -DRB1. In total, we analyzed data from 3460 patients. With multivariable adjustment EFS (HR 0.86, p = 0.003), OS (HR 0.82, p < 0.001), and risk of relapse (HR 0.84, p = 0.018) were significantly better for HLA-compatible UD compared to MSD. No survival advantage was found, when UD with unfavorable sex or CMV constellation were compared to MSD with favorable constellations. In a meta-analysis on 9905 patients with myeloid malignancies, including ours, we found reduced risk of relapse (pooled HR 0.78, p = 0.006) and better EFS (pooled HR 0.89, p < 0.001) for young matched UD versus MSD. To select young HLA-compatible UD over older MSD may reduce relapse risk and improve survival for older patients with myeloid malignancies.