In terms of "ruins your life", anything past a few years does that.
Speaking purely for myself, I don't feel much difference in the deterrent effect from the punishment being 5 years or 25 years. Either one would utterly wreck everything about my life, and although the latter is worse it's not enough so to change my decisions.
If he gets out in 5 years he'll be doing the same thing. He showed no remorse or understanding that he did anything wrong. A 25 year sentence means we've got 20 more years of public safety.
Speaking purely for myself, I don't feel much difference in the deterrent effect from the punishment being 5 years or 25 years. Either one would utterly wreck everything about my life, and although the latter is worse it's not enough so to change my decisions.