Born into a wealthy family in Orbois, a part of France noted for a number of isolated chateaus, Lili, called by most as The Mischievous Lili, is known for her effervescent, cheerful and playful personality, and her love of playing jokes (sometimes in her early years some rather dirty tricks from time to time) at sometime her family suffered a major financial setback and find they can‘t keep to themselves as they had been doing and find they need to go out into the world seeking wealth.
It’s decided by her sisters Elizabeth, Alice, Amelia, Elise, Marie, their tutor Mr. Minet, and her often traveling parents that Lili is the most qualified to do this, and thus her adventures start.
Eventfully Lili is supported by Dan, her American fiance, as well as finding she has to contend with her dastardly cousins, a jealous and deceitful mother and daughter team from nearby St. Herbu.
During her adventures Lili would work in a zoo, the circus (and encounter talking animals) as a model, a script girl in Hollywood, run with bandits in Spain, discover still living dinosaurs, act, find herself lost on an unknown island in the Pacific, travel to the Moon, works as a maid, take part in the Olympics, travel to dozens of countries, and gains a remarkable talking parrot companion, and never ever marry Dan.
Seemingly around 12 years of age just before her adventures start in 1909, and no more than 16 when she goes out into the world, she and her family change with the times, but age little so that by her last recorded adventure in 1998 she appears to be no more than 25 at most.
Not immortal, but it would seem certainly long lived, this is never addressed in the stories its just accepted as how things are, of note, as soon as Dan hooks up with her he too seems to age little over the more than fifth years they are engaged.
This is just unconfirmed speculation on my part, but I have to wonder if it has anything to do with a long story arch where she spent a great deal of time on a lost island in the Pacific. Just thinking out loud.