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.
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.