This is very close to my experiences with people, too. I've had varying results while trying to work on it and become more assertive. Some have worked, some still hang in the air, somewhere over Lake Michigan....

Something I know I had to work on was not letting things pile up, and then getting frustrated, and perhaps over-reacting. I've been working on giving a more measured, rational response when someone has crossed a boundary with me. That's been the best tactic for me, so far.

I also try to give people a chance to explain their position if I find there is some friction happening. That gives me a chance to hear their point of view, before it all evolves into a misunderstanding, and emotions get tangled, or responses get misconstrued.

Older people can be tricky to deal with, I've found. There's actually so much going on underneath that surface, that I've found it's akin to walking into a mine field. This is situation where it's probably the most important time to become a good listener.

If you suspect it's a case of people simply using you as an excuse to vent their anger, it is permissible to remind them that they don't get to do that. They need to justify that to you somehow, and back it up with an explanation. They have to give you a chance to respond. This gives everyone a fairer chance to be heard, and understood.

Great help from the Mayo Clinic: Being assertive: Reduce stress, communicate better - Mayo Clinic

Best of luck with it all.