I’m sure that God forgave you when you celebrated the Sacrament of Reconciliation many years ago. However, the fact that the act of taking money from another still bothers you after all these years indicates that there’s an additional step that you need to take before you can feel completely at peace. When we harm someone it’s important to make restitution, that is, to repair as much as possible the injury we did to the other person.
The first step is to make an attempt to pay back the person or institution from whom you took the money. This doesn’t have to be done openly, but can be in the form of an anonymous donation or secret gift.
Of course, after so many years the person from whom the money was taken may have died, or may be impossible to locate. In that case, restitution could be made to the person’s family. If even that is impossible, you can make a charitable donation, giving to the poor the amount you originally took. Once you’ve done this, you’ll begin to feel that the unfinished business you’ve carried with you for so long has come to a satisfactory completion.