I just got here at us may 24 2010 and now I'm a green card holder, I want to know if I can travel outside the us though I'm 9 months green card holder cause somebody tell me that in order to go outside the us I need to stay here for 1 year.

If your trip is a short visit, less than 6 months, it's OK.

Agree with lawanwadee. OK for travel now. No need to wait any set time after LPR approval.