1. An image processing apparatus, comprising: a face detection unit that detects a region including a face of a subject in a target image, as a face region, using data of a captured image that can identify a capture date thereof, as the data of the target image; an age recognition unit that recognizes age of the subject in the target image based on the face region detected by the face detection unit; a similar image search unit that searches for data of an existing image having a face region similar to the face region detected by the face detection unit, as data of a similar image, from among data of a plurality of existing images that can respectively identify capture dates thereof, each of which belongs to one of a plurality of groups; an age confirmation unit that confirms whether or not the age of the subject in the target image recognized by the age recognition unit is within a first range; a comparing unit that, in a case in which the age confirmation unit confirms that the age of the subject in the target image is within the first range, acquires a difference between a first capture date of the data of the target image and a second capture date of the data of the similar image found by the similar image search unit, and compares the difference with a second range; and a grouping unit that classifies the data of the target image into the same group as the group to which the data of the similar image belongs, in a case in which the difference is within the second range, as a result of a comparison by the comparing unit.