The Question and Answer section for The Immortal Life of Henrietta Lacks is a great resource to ask questions, find answers, and discuss the novel.
Lacks' cells were taken in 1951. As of 2015, they would have been sixty-four-years-old.
Skloot notes that like guinea pigs and mice, Henrietta’s cells (HeLa cells) have become the standard laboratory workhorse.
I think around 62 years old.