If the offender repeated the crime while being older than 25, then no. There is no realistic hope that the person will ever be non-harmful. Never let them free.
(cases between those two extremes are questionable)
And why start with a semantically negative presumption, anyway? A world of difference in attitude can be reaped from daring to ask whether a person might harm again, rather than if they will "ever be non-harmful".
Get in to a drunken fight at the bar on night... Life
Shoplift a pack of gum.... Life
WOW....
So it's actually like this:
You reach 25. You assault somebody. You serve time in prison. (now a questionable case) We decide to give you a second chance. You feel no need to follow the law, and you enjoy assaulting people, so you do it again. OK, at this point we know what kind of person you are. You didn't just make a bad decision one day. Simply letting you out into society is pretty much the same as assaulting a random person, because that is clearly what you are going to do.