I'm going to be slightly rude to an older woman who constantly shows up too early.
Why do you want to be rude to an old lady?
Because she's annoying me. She always wants to come earlier than the appointed time.
This is just a minor annoyance, there's no need to be rude about it. You should be respectful to the elderly, not mean.
I don't give a shit about the elderly, or about anyone for that matter. Especially those born before the year 2000.
You don't have to care, but you can express displeasure without being rude.  Ask her polite to arrive closer to the appointed time.