This article focuses on the receptor side (company employing for a trial) and glosses over the donor side (organisation that loses/offers the person for trial). Universities aren't affected by students taking internships over summer breaks, and are hardly affected by students inserting internships during semesters. However candidates at later stages of life are likely to either have an employer (who is likely to incur disruption and have little incentive for allowing extended leave), or be unemployed (which makes them less attractive for receptors).