Vania is 21 years old. She's also a virgin, not exactly a pure one though. She's a virgin filled with lust. She has never acted upon her lust though. Which is part of the reason why that when she died, she ended up in Lucifer's domain, Hell.
Lucifer is the king of Hell. The moment he meets Vania he knows that his life now has more amusement in it. He knows nothing of love, only the Seven Sins. So, maybe Vania can teach him a thing or two. Especially since her only sin is lust. ;)