I doubt that I'll retire by choice. Two divorces chopped my 401k in half, twice. I had a stent put in at 51 and two veins in my legs glued shut last month. My maternal grandmother died at 52 with a bad heart. I have my problems. My 33 year old half brother is the picture of fitness except for the bad heart that caused his doctor to say that he'd be lucky to live into his 50's.
Despite that, I'm putting the equivalent of a full-time, minimum wage job in my 401k because I might goof around and live, or become disabled and need it. Both of my parents became disabled (Dad Fibromyalgia/Mom mini strokes) before they could retire. If I don't live, my 35 year old half-sister will get the 401k, life insurance, and house. With that, and what she has, retirement will be possible for her, and her fiancee.