Okay, I was born in the Midwest, raised in Arizona, but have spent 20-plus years in Texas. Very few educated Texans say "y'all" when referring to one person. Many, if not most, educated Texans do use "y'all" when referring to the second person plural. It is actually a pretty useful term (I'm tempted to say "downright handy!").
When a client of mine from New York told me he had lived in Texas for 3 years, I joked, "Long enough to know the meaning of 'y'all'." He answered, "I even know the plural of "y'all." When I looked puzzled, he told me, "All y'all."
"All y'all" gets a laugh from us Texans.