If anyone had doubts about rapid growth in the virtual worlds sector of cyberspace, this should clear them up.

There are more than 150 virtual worlds -- either open now or in development -- targeting people 18 and under, according to Virtual Worlds Management (VWM)  This is up from around 100 just last April!  Worlds for tweens (ages 8-12) lead with 88. There are 72 worlds aimed at kids (ages 7 and under) and 60 targeting teens.

In all, there are 95 youth worlds currently live, reports VWM, with another 68 in concept, development, or testing phases.  Disney alone has nine in development! (You should note, however, that the definition of "virtual world" seems to be broad; I noticed one site that's largely avatar chat, not strictly an entire "world.")

The New York Post cites eMarketer research showing estimates that "more than half" of all online youth aged 3-17 -- about 20 million young people --  "will visit virtual worlds by 2011, up from 34%, or 12 million, this year."

In an analysis of the VWM report by its authors, Craig Sherman, CEO of Gaia Online, a world targeting teens, discussed worlds "aging with their users."  He told VWM that 30% of Gaia users were now over 18 and the site had, "accordingly, grown a little edgier."  This is undoubtedly inevitable -- since users won't drop out of a site simply because they turn 18 -- but it does call for parental caution for younger users of such "aging" sites.