People are nuts, how is Joanie any less dated as a name? It's more old lady than Joanne or Joanna.
Also why should the fact people don't "know anybody under the age of 40" be a reason not to make a child that. I'd say it was an even better reason!
Joanna is nicer than Joanne. (And for the record I know a Joanne born in the mid-2000s).