His certain set of skills hasn't dulled a bit and he's still killing people that deserve it.
Like him, they're secretive killers whose homes are rigged like fortresses beneath a creepy facade, and who relentlessly hunt trespassers who try to steal their rumored hoards of wealth.
- Even moreso, they both have large vicious Rottweilers as guard dogs.
His years of fighting crime in Hell's Kitchen has slowly wore away at Daredevil's refusal to kill, and now he's taken after The Punisher by killing those who deserve it, including people who try robbing him.
- Alternatively, he is Stick. They even look alike.
The Blind Man is a Vietnam veteran.
This is why he's so familiar with guerrilla techniques, as well as combat in general, and explains his willingness to terrify and kill intruders. In addition to this, his blindness was caused by cataract, which means he would've lost his sight gradually and thus he adapted as he lost his vision.
- Jossed; he's an Iraq veteran, and his blindness was caused by grenade shrapnel.
Somehow he got blind but his skills in stopping "Home Invaders" are still sharp as ever. And it's not entirely out of the question that his past childhood trauma turned him into a killer.
His advanced age and blindness may have made him a far more subdued man in terms of demeanor, in addition to forcing him to retire from mercenary work, but his ferocity when it comes to combat has been anything but dulled.