Internships are considered "high-impact practices" offering students transformative opportunities to develop new skills and professional identities while immersed in workplace culture. They have also been pinpointed as key to improving student success and employment within science, technology, engineering, and mathematics (STEM) fields. However, much of what is known about internships has centered around the experiences of adolescents pursuing traditional academic paths, despite the presence of many nontraditional adult degree-seekers in higher education. As the STEM pipeline yields to a "pathways" approach and an evolving high-tech economy demands increasing flexibility and worker mobility, stakeholders must consider the impact of age on the internship experience from entry to exit. This exploratory dissertation in practice does this by identifying common challenges encountered by adults pursuing internships and examining ways in which their life course trajectories and structural internship features interplay to create them. Data gathered through semi-structured interviews of 13 adult undergraduates pursuing STEM careers and interning with the National Aeronautics and Space Administration (NASA) is approached through a life course theoretical lens in conjunction with the Internship Process Model developed by Hora et al. (2020a). Thematic analysis reveals common patterns in the experiences of adults throughout the internship process which fall into the overarching categories of challenging logistics, social marginalization, and a deficient recognition of work history. Based on these findings, recommendations are offered to develop a NASA Internship Program which is more accessible and inclusive for an increasingly age-diverse student population. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]