If you don’t want the value to be changed after rejection, you should control it manually, there is no such feature in the system for now. You can export your data and keep track of age question outside of Survey Solutions and make sure the value doesn’t change over time.
Sitanshu, after the interview is submitted (=completed+synced to the server) neither the interviewer, nor the supervisor can change the answer that has been recorded. Except the case when the interview is rejected, but that is the whole point of rejection to be able to make changes.