"It Sir-tainly isn't up to me!"

Ever notice how familiar we have become in addressing other adults whom we have just met. When I meet clients for the first time I still like to use the Mr. or Mrs. (if I’m sure she’s the missus). As a young girl, meeting my boyfriend’s elderly Aunt and Uncle, I called them Mr. & Mrs. So-and-So. The lady quickly encouraged me to call her “Cookie” – which felt awkward for me. I know she was just trying to ease my nervousness - it did throw me for a loop though. I’m wondering if I’m just plain old-fashioned or if this common practice of addressing someone on a first-name basis right off the bat is just a bit presumptuous?