In order to address the issue of age differences in feedback reception, this study investigated the effect of recast in task-based grammar instruction on Iranian adolescent and adult EFL learners’ learning of conditionals and relatives. The data were collected from 114 adolescent (aged 15-18) and adult (aged 30-35) EFL learners. Of the two adolescent classes, one class was assigned as the experimental and the other as the control group and the same procedure was followed for the two adult classes. The two experimental groups were provided with recast. The analysis of the participants’ performance on the posttest demonstrated that the experimental groups outperformed the control groups, and adults more than adolescents benefited from recast. As a result, the efficacy of recast in establishing new grammatical knowledge was proved. Further, the age of the learners did affect the degree of the utility of recasts in developing grammar knowledge.