(*answer refers to the wife of Henry VIII, not the actress born 1951)
She was either 27 or 28 when she died in 1537.
It was believed that she was 29 because she had 29 attendants in her funeral line.
"Her exact birth date is debated; it is usually given as 1509, but it has been noted that at her funeral 29 women walked in succession. Since it was customary for the attendant company to mark every year of the deceased's life in numbers, this implies she was born in 1508."
Jane Seymour was the third wife of Henry VIII of England. She was born in 1508 and died on October 24, 1537, soon after giving birth to Henry's only male heir, Edward, on October 12. If the 1508 birthday is correct, she was likely 29. If the 1509 date is correct, she was likely 28.