From Andragogy and Self-Directed Learning: Pillars of Adult Learning Theory, a chapter by Sharan B. Merriam in New Directions:
“The five assumptions underlying andragogy describe the adult learner
as someone who (1) has an independent self-concept and who can direct his
or her own learning, (2) has accumulated a reservoir of life experiences that
is a rich resource for learning, (3) has learning needs closely related to chang-
ing social roles, (4) is problem-centered and interested in immediate appli-
cation of knowledge, and (5) is motivated to learn by internal rather than
external factors.”

I wonder how much #2 can also be a barrier to adult learning? For instance, I work with teachers who have a rich reservoir of experience of enduring really bad professional development. Some of what I do is try to earn their trust by trying to understand their context and concerns and letting them know that, while I have an agenda, it can be modified as needed to meet their interests. I try to customize as much as possible.

Later:  I am reading Knowles’ New Perspectives on Andragogy and he discusses this very issue, noting that a learners’ experience can create biases against learning.  He says that this issue has been the subject of much recent research.  He goes on to discuss Senge’s work with mental models.