First I must say I don't know how to explain my background context without it sounding very condescending, I just suck at words and don't know how to do it, but please know that I mean it in the best way possible, when comparing my work with dementia patients to your congregation. It's just that my work with dementia patients taught me a lot about humans in general.
I worked with lots of very elderly people with dementia as a caregiver not that many years ago, and it took me a good little bit to find a smooth navigating process when it came to both respecting their dignity and getting them to cooperate, at the same time. It was a very similar sort of situation, in the sense that I needed them to listen to me for their own well-being and safety in several regards, but I was also just a young whippersnapper while they had lived very long, rich and often impressive (in various ways) lives and were not about to take 'orders' from me. And that's what I didn't realize was going wrong at first. I thought I was doing well by being very clear and direct, but that is not how they were perceiving it, and the latter is what mattered.
So trying to translate what I learned about medical/physical caregiving, into the direction of spiritual caregiving, my advice is to take whatever has their feathers ruffled and turn it into a strategy. It's possible to be genuine and speak the truth, while still having a motive.
Like for example, in a grateful tone, you could acknowledge that this is a rare and very valuable opportunity, to combine the wisdom of the elderly (or whatever word doesn't offend them in some way) with young ministry fresh to the calling, and ask them to help you make sermons more like a discussion so that as you share your insight, they can also share insight with you, and then at the end, you pray with them altogether that you all are able to absorb each others' wisdom of the Word.
This approach attempts to tap into the underlying emotional needs and vulnerabilities (which are fairly common and normal) that they seem to be expressing:
1. They want the venerability of their old age and acquired wisdom to be acknowledged and respected.
2. They want to teach you things and pass on wisdom to you (even if you don't agree with all of it).
3. They don't trust you enough to be able to just sit back and mindlessly absorb whatever you say.
4. A very young and culturally unconventional pastor giving them direction is likely just one of many little stings they likely feel when it comes to growing old and being regarded as irrelevant, outdated and therefore treated with less dignity by much of society. (Some of them have likely known friends or family who were put into homes like putting a vacuum into a closet, and maybe they don't want to be condescended or invalidated or figuratively shoved aside and replaced in the last social setting many of them have - their church.)
If you can figure out the underlying sensitivities that they are experiencing, then it can help you come up with a strategy that is empathetic towards those sensitivities, while still getting the important part of the job done. Maybe the first X years of pastoring at this church, with this crowd, it won't be quite like you might have imagined it, but you can still get them to focus on the scriptures and what it means for their lives and their souls and thus motivate teaching, learning and fellowship. Sometimes my especially feisty residents/patients came to breakfast dressed in all manner of uh, interesting outfits - but they were clean, they were comfortable and they were happy.
