From Second Life Wiki
A newcomer to Second Life or Teen Second Life; a Resident who has joined for a relatively short period of time and/or is not familiar or comfortable with Second Life’s culture, interface etc. The newbie cut-off point is generally considered to be at around 90 days. It is possible to still be widely regarded as a newbie if you are older than 90 days old if you do not act your age. Using AOLisms in the metaverse's local chat (such as "u" instead of you, "ur" instead of "your" or "you're" or LOL instead of "/me laughs") or lacking knowledge otherwise expected of someone 90 days old will generally cause one to be accused of being a newbie regardless of age.