Many writers employ an interviewing technique in order to give characters depth and realism within a plot. This makes sense to me and is a solid practice for creating deep, meaningful characters that foster realistic relationships within the prose.
My question is regarding characters who age noticeably throughout the course of a single novel. My specific example is a protagonist who is 25 years old in the first act, and after a gap which is not directly portrayed, is 46 in the second act. To add to this, there is also a potentially life changing event planned for the first act.
Should I interview this character as a 20 year old, a 40 year old, or at both ages, as separate interviews?