Say an unmarried Baal Teshuvah at the age of 30 decided to make repentance. A lot of time has gone by and he doesn't remember who he cheated, lied to, stole from, spoke loshen hara about, and so on. ...
The Father (not frum) of a Baal Teshuva asked his son for a loan. The son agreed to give his Father the loan on condition that he starts to keep Shabbos. Is this a problem of ribis?