I SO believe in boundaries! I have no problem telling people that something won’t work for me or that I would rather not do something. Perhaps it comes with age but I find that my time and energy are important and doing something that drains them is not what I want or am willing to accept.
When you let people know the truth, I think they respect you more. I know a person who always says yes to everything even though they don’t want to do it and to me that isn’t being honest/truthful and in the long run you will become resentful.
Teach people how you want to be treated by deciding what you will and won’t accept. Let them know!