What is Dr. Kureha's secret?

Question

In the Drum Island arc, Dr. Kureha always asks this:

So, what is the secret of her youthfulness? Is it because of her medicine? Her lifestyle? Maybe she found a fountain of youth?

Answer 1

There is an interesting theory about this.

• In an interview Oda said that normal human can only live for 140 years in One Piece.

• How old is Dr. Kureha? In a scene before the timeskip, she said that she is just 139. That means that after the time skip, she must be 141. Beyond what Oda said is the limit of a normal human!

• Now let's remember this moment, when the "Ope Ope no Mi" fruit is introduced. Here it was stated that he with the powers of this devil fruit could perform the "Eternal life operation", which would provide eternal life to the patient, in exchange for the doctor's life.

So, the hypothesis emerges...

What if someone performed the "Eternal life operation" on Dr. Kureha in the past?

As you have seen, in multiple places during the manga, she asks "You want to know the secret to my youth?"

This was always thought to be a recurring joke, a comical relief, but... what if there was more behind it that it seems? Oda uses to make this kind of things A LOT.

Only time will tell... ;)

Answer 2

She being a doctor, must have found some medicine which she drinks from her beer bottle. Also she was the first one to mention the will of D and she knows the actual name of Gol D Roger, shows that she actually must be around 140 years of age.