Stemless shoulder implants have been introduced to prevent some of the complications related with the stem in total shoulder arthroplasty and reduce stress shielding. Despite the general recommendations of good bone quality conditions from the manufacturers of these implants, little is known about the influence of bone quality on their performance. The purpose of this study was to investigate how aging, and the consequent changes in bone density, affect the primary stability of five anatomic stemless shoulder implants. The implant designs considered were based on the Global Icon from DePuy Synthes, Sidus from Zimmer, Simpliciti from Wright, SMR from Lima Corporate, and Inhance from DePuy Synthes. The virtual simulation of the stemless shoulder arthroplasties was performed in Solidworks. Medical images of a cohort of 20 subjects from two age groups, 20 to 40 and 60 to 80 years old, were used to obtain corresponding density distributions, which were subsequently integrated into three-dimensional finite element models of a single humerus geometry, developed in Abaqus. The Sidus, Simpliciti, SMR, and Inhance designs, which lack a solid collar covering the entire bone surface, were modelled considering two extreme contact conditions – contact and non-contact – between the humeral head component and bone. Micromotions at the bone-implant interface were used as a metric for primary stability. A statistical analysis of the results was conducted, using three research variables which considered 20 µm, 50 µm, and 150 µm as thresholds for osseointegration. The 60–80 age group registered increased micromotions due to the age-induced decline in bone density, when compared to the 20–40 age group. However, since certain designs presented good overall performance regardless of the osseointegration threshold considered, age alone may not be a contraindication to the use of stemless implants. This finding is particularly noticeable for the Global Icon-based and Inhance-based designs, which present the best performance, showing the lowest sensitivity to bone density. Whenever feasible, contact between the humeral head component and the resected bone surface proved to be beneficial and is therefore recommended.