I heard Aunt Tilly is 28 years old.
If that's what she said, then that's how old she is.
I learned long ago to NEVER argue with or question a lady about her age, and if you are forced into a position of having to guess then NEVER make a guess above half her obvious age. Doing anything else makes one risk being the recipient of her everlasting wrath, which can manifest itself in astonishingly wide-ranging, catastrophically expensive, breathtakingly painful and occasionally lethal ways. I can think of a million better ways to die than what such a scenario would visit upon me.