The question is rather broad If you mean the full depth if the mortar joint lime& sand mortars in U.S. ( colonial williamsburg)are 250 yrs.and are just now recieving their first pointing! Castles in europe also using lime mortars are 1000+ yrs. However these walls have been repointed at some time. I would say most mortar exposed to severe weather will still be intact for 100 yrs.+ if it was made right. You must understand mortar is the sacrifical element in ALL masonry walls. When the face of the mortar erodes approx. 1/4 inch it should be cut back as deep as the joint is wide and new mortar of same type should be used to fill joint flush with face of wall.