Discounting the Parallel story, we see Chibiusa as a teen two times in the series.

In Sailormoon R, She becomes Black Lady after she runs away with Wiseman. Feeling lonely and unloved, she keeps the Silver Imperium Crystal for herself, but due to the dark energy of being Black Lady, she is unable to use it. In the manga, she kidnaps Mamoru, posseses him and actually kisses him. (SPEEEEEEEEEUUUUUUUUUWWWWW!!)
Her reign of terror comes to an end, when Diamond tries to have the crystal of "our" world and the 30th Century crystal meet. Then, Sailor Pluto gives her life in performing the ultamate taboo, stopping time. So heartbroken by the loss of her friend, Chibiusa's power breaks the hold of the dark energy, and allows her to revert to a younger state, (though still much older) and become Sailor Chibimoon.
As seen here:
In the anime, she doesn't realize that she even has the crystal, until she reverts back to her normal self. And afterwards does not become Sailor Chibimoon until Sailormoon S. As Black Lady, she terrorizes "our" timeline's Tokyo, and frequently hopscotches back and forth between timestreams. Sailor Moon opts to use her crystal at least 2 times to heal her daughter, but to no avail. After Sailor Moon turns into (or fuses with if you will) Neo Queen Serenity, she helps Black Lady through her memories. Black Lady sees what her parents were trying to teach her, (By not being caring, supportive people, mind you) and decides the warm feeling in her chest is not the crystal, but in fact her love for her parents and in return, their love for her. She then reverts back to little girl mode. (Insert *Gaaaaack* here.)

She ages again when Palla Palla switches Chibiusa and Usagi's ages in Sailormoon SuperS. Though still innocent, the others are obviously warey of the adultisized Chibimoon. (For fear she has become Black Lady again.^_^) Although this is her dream (and Helios's as well-.-), Chibiusa realizes right away that this is not her true form, and is quite pleased when she reverts back. An interesting factoid here: In the manga, Helios was rather turned on when he saw his maiden as an adult, however in the anime, Helios was taken aback by the matter, and was soooo happy when she reverted back, that he snogged her. Whether you believe that it was only the black magic that freaked him out or not, one can't help but notice that whomever wrote that should NEVER be allowed to hang around kids! >_<

Ultamately, Chibiusa will one day become the maiden Helios searched long and hard for, and on that day, she will live up to her given name of Princess Lady Serenity, and will one day rule as the next Neo Queen after her mother.

A princess yet a soldier with a beautiful dream, protected by Moonlight, the maiden who posseses the crystal to break the seal of the Golden Crystal.~ Helios, Sailor Moon SuperS graphic novel # 3, Tokyopop edition.