There are a few different things going on here. If you feel 'bossed' by AC's, that you are bending over backwards helping with them with childcare but doing everything wrong and being ordered how to do it, don't do it. No conflict necessary, find a way to enjoy time with them on your own terms.
One of my relatives calls her kids "the children". The youngest is 50. Infantilising works both ways.
This whole thread reads like communication problems on both sides. Seeing our DC as adults can be tough, accepting that you are no longer the dominant force in charge and they have their own ways can be tough, simply accepting that you're ageing can be extremely tough. The amount of people who post on MN because others parent differently is constant. Terry v disposable, breast v bottle, natural v c section, WAHM v SAHM, state v private, meal planning it goes on and on. When it's your own AC who aren't making all the same choices you did and asking you to do things differently it's bound to be doubly frustrating, it challenges everything we think we know and that worked for us. But It's not about keeping your lip zipped, it's about adjusting and accepting that people aren't carbon copies of yourself, and relaxing your iron grip. Relationships change as people get older, its the natural order of things, and fighting for control of that or never ends well (if you think it does, there's likely a person avoiding you as much as they can or privately on AD's & having counselling sessions).
OP if you are only 60, close to my age and not remotely close to 80, your GC will be adults themselves by the time you're that age. You are worked up and pre-angry over something so far off in the future that it's all a bit of a stretch.
To refuse to plan for your elderly years in order to be contrary is just daft.