Forever Young?

At what age does it start being flattering when people think you are quite younger than you actually are? Whatever age that is, I haven't reached it yet. I helped out with VBS at WAG today, and toward the end, I introduced myself to another woman who was helping out and sitting behind me. I introduced myself by my first name, and was slightly taken aback when she made it a point to introduce herself as Mrs. ___________. I immediately assumed that she had assumed I was a teenager, so I made it a point to tell her that I teach English at the school the church supports. She was shocked, then noticed my wedding rings. She apologized a bit and re-introduced herself by her first name. She told me I was lucky. I'll be lucky in six or so years when I'm thirty and people are thinking I'm young, but it's not so flattering as a twenty-four year old to be mistaken for an eighteen year old (or worse, twelve; I've gotten twelve before).