because I set the example with them.

In my area (southwestern Mexico) we use "tú" for almost everybody right away. If they are older or in a position of authority, "usted" is better initially, but almost invariably we move to "tú" quickly -- upon second meeting, for example. The only exception I can think of is if they are older AND in a position of authority -- then we are likely to remain with "usted" indefinitely.

"Tú" is also used on billboards and official highway signage here.

My cleaning ladies, who I'm pretty sure are from Mexico, absolutely use it with me. I can speak a very limited amount of Spanish, and I love getting the practice.

It helps to keep in mind that Spanish varies enormously, not just in vocabulary but in grammar and usage, from country to country.

The French are generally far more uptight about using the familiar you. In French it's also tu, and the formal an normal you is vous (pronounced "voo", rhymes with boo.) Adults can use tu with children and others below them in social standing, but everyone else is vous.

One downside of the French I took in the 1960s is that we could conjugate verbs by rote, but never ever used tu in the classroom. Even the teacher, who I think in France would have used it with us, always used vous. Once, I was visiting a French family in Paris, and the four-year old in the house addressed me as tu (which was actually appropriate for a child that young) and I had trouble understanding her, because I couldn't quite catch the verb form that went with that pronoun.

First name only use tú
Title plus first name or title plus last name use usted.

Usted is actually a contraction of vuestra merced "your highness"

People are usually very patient with newbies and will simply request you to use the other form.

They never taught that about usted back in high school.

Some of that rubbed off.