There are certainly arguments to be made for both sides of this question.
It is possible to argue that people do not change. We can say that a person who is willing to commit criminal acts has, in some way, a fundamentally criminal personality. We can argue that, for example, they may seem to have reformed when really all that has happened is that they are in different life circumstances that allow them to seem different. For example, a person may have appeared to have turned their life around in prison but that is only because they have fewer chances to commit crimes and/or because they are trying to appear reformed so they can get out earlier.
On the other hand, we can also argue that people change. We can argue that people mature as they get older. Their life experiences teach them that they need to be more concerned with the needs of other people, for example. This could lead us, for example, to support the idea of rehabilitating prisoners in hopes that these new experiences could fundamentally change them.