Dr Bonner was 104 when he perfected his alchemy experiments and developed a version of the elixir. Knowing his time was running out, the good doctor drained his vial, and then suffered incredible pain as his body morphed, bones crunching and shifting into a smaller female frame. His withered wrinkled flesh filled out with the bloom of youth, and his body developed breast and a female slit, replacing his manhood in a period of minutes.
When the process was done, the doctor dressed in a red corset and stockings, and then parched on the edge of her desk, staring into space. She had managed to roll the clock back 80 years, but at the price of her maleness. And there was no way she was going to let the effects wear off to try a modified elixir. She was stuck as a young woman, a very honey young woman, with decades of suppressed sexual desire to express.
The man who could cheat death was no more; now there was a woman who could cheat death instead.