"Two possibilities exist: either we are alone in the Universe or we are not. Both are equally terrifying." -- Arthur C. Clark
The gnome hefts the giant tome situated on his back and then pushes his round spectacles up his protruding nose. He rubs the tip of his nose, knowing that he should really stop studying with his face so close to the books. The skin would sometimes rub off the tip during long hours of recording and study. Specks were moving on down the road, and he produces a spyglass from a loop on his hip. Through the lens, he spots a group of adventurers. He grins from ear-to-ear and gives a hoot, almost losing his balance due to the weight of the book on his back.
"These fellows look like they have purpose! It's time to find out what they're up to!"
A race of beings actually IS invunerable while in adolecence. They age, but cannot be killed. A miniority of the race (1 in 20) does not become invunerable, but rather becomes immortal at some point in thier adolecence, and ceases aging while being vunerable to death in all the normal ways. Another minority (also 1 in 20) Permanatly becomes invunerable after adolecence, but ages twice as fast as the race normally does. There is no known way to test for which of the three traits an individual manifests and the three traits cannot mix, as they are tied to the same gene, as it were.