I have done a lot of crazy things in my life and continue to do so, even though I hit 70 next January.
Apart from breaking the speed limit from time to time in my youth when driving, I have done nothing illegal.
I think the word 'sin' is a misnomer, when attributed to the Bible it often includes things which no decent person would consider wrong, like homosexuality and sleeping with your partner before marriage in a committed adult relationship.
One cannot repent of things one doesn't think one did wrong. One can only change one's mind about whether that was wrong. If you become convinced that it was wrong, then 'repenting' means 'well, I didn't know better then, but I do now so I won't do it."
That's "repenting," too.
The stages of repentance, I have been taught, are these;
First be aware that one has done something wrong...or not done something right. Basically, be aware that one made a bad choice, even if it seemed fine at the time.
Second: regret the bad choice.
Third, if POSSIBLE and appropriate, make restitution and apologize to anybody who was caused harm because of your choice. That may just be you. If your choice harmed you, apologize to yourself, and change whatever needs changing. Forgive yourself.
Fourth: change your life so that you don't make those choices anymore. You may have to do these four things repeatedly until they stick; habits are hard to break.
Now, if one is an atheist or something else, steps one through four are sufficient. If one is a believer in an afterlife and a deity, step five:
Five: Ask God for forgiveness, using whatever prayer or ceremony is appropriate. Make promises to be better.
Six: If your religion does this, do whatever ceremony gets rid of all your sins commited before that ceremony. That's what adult baptism is for. Some faiths allow you to be baptized many times. Others let you get baptized (or whatever) once, but have something else that allows you to get rid of sins. Generally that's something like communion or something.
Seven: honestly work at improving yourself. Even the folks who believe in 'once saved, only saved,' believe in good works; only the motive ascribed to those works changes.
So, if there is an afterlife, that's what you do, according to every theistic belief system I know, and non-believers do steps 1-4. Generally.