The original Grandma Moses was about 80 when she had the first big showing of her primitive art. My first mystery was published by a small e-press a month before my 80th birthday. Now, at 90, I've published other books: more mysteries (one a YA ghost mystery), a book of ten short stories, and a non-fiction retelling of my father's adventures when he worked in Alaska for college money.
I'm currently working on a new series. If it works, it will be a series of novellas, sorta mystery, sorta paranormal, with a bit of time-travel thrown in
I've had short stories and articles published in children's and adult magazines in the past. More recent credits are an essay in the Sisters in Crime Writes of Passage, an Agatha winner for non-fiction of 2014, and a short story in the anthology, Fish or Cut Bait (now included in my book of short stories.)