An organizer of a campaign to put a marijuana-legalization initiative on the 2012 ballot said Thursday the measure would likely apply only to those over age 21 and would allow personal possession of only small amounts.

Brian Vicente, the executive director of Sensible Colorado and one of the voices behind the Colorado Legalization 2012 campaign, said the draft-initiative language would create a state-licensed system of pot shops, similar to the regulatory system for liquor stores, and would allow individuals to grow small amounts of marijuana on their own. He said marijuana sales would likely be subject to a special excise tax.

Details are still being worked out, Vicente said. The campaign has yet to file any initiative language with the state.

"We think it's got a really good shot of passing," Vicente said during a panel discussion at the annual conference of the National Organization for the Reform of Marijuana Laws.