What do you think of me telling my coworker she looks older than she claims?
Why would you say that to her?
She is rude and I want to test her reaction.
You shouldn't start conflict at your work. It is better to just let it go and not care about what your coworkers says about her age.
I just can't resist the urge. I want to start a conflict since I feel like she's giving me a lot of dirty looks.
Confront her about her rude behavior, not about her appearance.