If you find any numbers on this, I would love to hear the results of your research.
I’ve done a bit of research, and all I can find is anecdotal info. I did speak with Mary Jane D’Arville, co-owner of the Virginia Harp Center. She has observed a growth trend in the number of adults taking up the harp once they are adults. She says that is, in part, what has driven the development of so many new harp models in the recent years—more models to accommodate adult students.
She is also co-organizer of the Beginning in the Middle,