no you most absolutly do not need a license to give lessons i wouldnt suggest giving lessons until you yourself have at least 5 yrs under your belt,(im assuming of coarse that you do have expeirence) . one of the most vital things about teaching guitar is making sure you dont restrict the student to playing a certain style of music or a certain brand of guitars also making sure they dont pick up terrible habits. i hope this information helps

You do not need a teaching certificate/license unless you want to teach in a state-accredited educational setting.