Interesting one again Ephie.
For me, ideally, the role of the mother of adult children would be as a the mentor that knows you, that 'gets' you. Someone who you can turn to for advice, to vent, to share-- part friend, part advisor, part sounding board. Someone who understands and remembers the traditions that you want to remember, and who is flexible in understanding that you'll want to form your own traditions too. Hopefully, the mother is able to enjoy the good things in their adult child's life right along with them, and who would want to augment the child's life and relationships (for example, to get along with daughter and son in-laws and extended families, enjoying grandparenting, etc.) without taking away from it with drama or their own unmet needs.
Please know that I'm thinking, too, of a middle-aging mother, not an elderly mother. I don't really know what that looks like, or what the expectations in those relationships need to be.
I do not have any sort of real relationship with my mother at this point. She and I have issues from our past which she doesn't want to address, and due to the nature of those previous issues, being in relationship with her is pretty emotionally dangerous for me. I feel very fortunate, however, in that I have seen people I truly admire as parents grow into the role of being a parent of adult children. I am encouraged by the camaraderie these moms have with their adult children, their way of caring without being intrusive or helicoptering-- it's lovely.
My son is five, so no, we don't have that sort of a relationship in the same way we might when he's 25. That said, I'm laying the foundation for that sort of relationship now: being honest, answering his questions when he has them in a simple way, trying to own my own emotions when conflict arises, listening a lot, doing simple things for him to show him I am paying attention and that I care. Letting him know that I like him and that I do very often enjoy his company. Finding out what he's interested in and participating in some of those things, even if it's just sitting and coloring a picture with him. I want to be like that comfy pair of sneakers for him when he's an adult-- someone he can trust, feel secure and accepted with, and who he can let his guard down with. That would be great.