That depends on the individual. For instance, let's say somebody did something to a kid while babysitting 15 years ago. Now further assume that this person went to prison for 5 years, and was brutally mistreated by the other inmates, while the guards turned a blind eye. And even though this person has been through hell, they get out of prison, go to therapy, get a job, and never hurt anyone again. Are you telling me that this person should pay in 2018 for what they did in 2003? How long must they keep paying? According to the US government, the answer is for the rest of their life. Because guess what? They have to register every year on their birthday, and every time they move, switch jobs, or take a class at the local community college. They will never be able to get a job at Home Depot, Intel, Target, Walmart, or most other big corporations.
You may not care about that, and society wouldn't blame you a bit, but how much punishment is enough?