1) In Princess Cookie, she visited the Candy Orphanage. Baby Snaps was still a kid there, and Bubblegum looked 18. It was the past. While Cookie has grown physically, PB still remains the same.
2) In the promo art for Burning Low, Flame Princess seems to very young, like 5 years old. While Peebles in next to the lantern, looking 18 years old.
3) In The Suitor, the oldest suitor said he had been waiting for PB for 300 years. Indicating that she has lived for 300+ years. I think that it is because of Candy Biomass that makes her live.
(Back where we left off)
Flame Princess: Well...
Finn: I got to go
Flame Princess: Finn wait!
Princess Bubblegum: So you found out huh
Flame Princess: You! (Has a fireball ready)
Princess Bubblegum: I'm not here to strap you up
Flame Princess: Then just run away like the others (Looking sad)
Princess Bubblegum: Finn isn't going to confess right away
Flame Princess: Then when tell me when!
Princess Bubblegum: Time will tell you the answer, well I have to get going the candy citizens are going to be protected on their own, Morrow! (The bird takes her away)
Flame Princess: Oh Finn tell me please
(She walks to the treehouse and Finn opens the door)
Part 3 coming soon! Keep watch citizens ^-^
Flame Princess: Well...
Finn: I got to go
Flame Princess: Finn wait!
Princess Bubblegum: So you found out huh
Flame Princess: You! (Has a fireball ready)
Princess Bubblegum: I'm not here to strap you up
Flame Princess: Then just run away like the others (Looking sad)
Princess Bubblegum: Finn isn't going to confess right away
Flame Princess: Then when tell me when!
Princess Bubblegum: Time will tell you the answer, well I have to get going the candy citizens are going to be protected on their own, Morrow! (The bird takes her away)
Flame Princess: Oh Finn tell me please
(She walks to the treehouse and Finn opens the door)
Part 3 coming soon! Keep watch citizens ^-^