Forum:Princess Bubblegum's age?

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Iv noticed that from season 1 up to season 5 Princess Bubblegum has not aged at all other than when she turned 13 in mortal recoil and then later turned herself 18 again and she still has not aged at all over the long period of time afterwards.

Does anyone have any theorys on how Princess Bubblegum has not aged at all through the seasons?