Another ditto here.

I can well remember the time in a coffee shop when I said "Yes, m'am" or "No, m'am," to a waitress who was young enough to be my daughter. After a few visits, she shyly said, "Sir, you don't have to call me 'm'am,' I'm lots younger than you."

I replied, "I was taught to treat all women like ladies until they proved themselves otherwise and then treat them like ladies anyway."

Same for using "Sir" as a term of respect. Just be glad they young men were treating you in a respectful manner, and enjoy it.