Referring to the topic above to Dr. Monzer Kahf, Scholar in Islamic Economics & Financial Expert, he said,

All properties that belong to others should be returned to them as a condition of repentance and seeking forgiveness from Allah. This has no age limit. Any thing that you know is not yours and you took it should be returned to their owners.
If you were forced to take to the benefit of others while you were a child and others took these properties, of course you are not responsible for returning them now; rather those who took them should return them. But if you took these properties to yourself and have spent them by now you have to return the equivalent.