Quite a difficult topic (both psychologically and ethically), especially if people are very close to each other.
If you care for someone and you see what you interpret to be suffering or making a mistake, it can be quite difficult to not give what you think is apt advice or intervene. Parents are a prime example of course. On the other hand, if the one receiving the advice interprets that things are getting worse rather than improving and attribute it to the bad advice or the person who gave it, it can feel like trusting that person was a mistake. Quite difficult. Personally it seems to me that it might be helpful for both to step back from the whole situation together and try and see what happened from a more neutral perspective. If both share a common goal and want to work together, I think a lot can be solved.
What I think is a bit simpler though is that I would not say that just because someone is older, their take on something is worth more than someone who is younger. I would say that if you yourself are less experienced in the matter than someone else, it might not be a bad idea to give what the other has to say some serious thought. That being said, it does not mean that you are wrong even if what you say diverges from what the more experienced person said. But people who are way more experienced often do seem to be relatively closed to new ideas. That is something I constantly experience in my work when what I say goes against someone who has been working on the topic for 30 years.
We should open a psychoanalysis thread or something