Wikipedia has this to offer:
"There are several possible etymologies for the word. It may not have been derived from a single source, instead evolving from multiple convergent usages. Its exact origin is unclear.

The gay-slang usage of "twink" has been suggested as a likely origin.[1] One of the unofficial connotations of this usage is "a young/inexperienced person who can outfit himself fashionably because of financial benefits from an older/experienced sugar daddy." This parallels MMORPGs, where in-game money is a strong limiting factor in the virtual economy and gear is usually in the form of clothing and jewelry.

The word "twink" appeared in the Ultima Online: Renaissance playguide in the glossary of terms. It was asserted to have a meaning similar to its current one, but also included powerlevelling.

On the MUD Sojourn, which several creators of EverQuest played, "twink" was alternately used to refer to powerleveling and metagaming. As MUDs date to 1978, this use of the term may possibly predate later uses."