I think it was just a name until Vladimir Nabokov wrote his book
with that title.
After that, it took on a meaning of "a pre-pubescent sexually
attractive girl". A more coarse term for it would be "jailbait".
It's still used as a name though.
Mostly, because of Nabakov's book, a man with a "Lolita complex"
would be an elder man who has an unhealthy and usually sexual
obsession with young girls, or a young girl.
