Who is making it? Who is not? We've concocted retirement scorecards for some showcase retirees in entertainment, politics and sports. See the full list here.

Loser: Sumner Redstone
Former occupation/notable position held: Controlling Owner (still active), CBS Corporation; Viacom (includes Paramount, MTV Networks, etc.)
Activities during retirement: Not applicable
Retirement Report Card Grade: D-

What keeps Sumner running? Why won't (can't) he just stop?

One of the great things about being a mogul: no mandatory retirement age. That's not a bad thing, as long as said aging mogul is still operating in the best interests of all of his stakeholders: himself, his family, his friends, employees, and public shareholders.

Much of this doesn't seem the case for Redstone, 85. His latter-day career highlights include a publicly waged battle with his daughter Shari, long named his heir apparent, over corporate governance and strategic issues. The battle has played out in the press, sometimes in brutally personal detail.

His refusal to cede control has cost him other dear relationships, like that with longtime confidant Tom Freston, widely credited as the architect of the modern MTV. Redstone ousted Freston as head of Viacom for reasons few in the know understood. And Redstone's public kneecapping of Paramount money machine Tom Cruise made Cruise's own infamous Oprah couch-stomp seem downright sane.

Redstone stays just a hair shy of a retirement "F" for one, purely semantic reason: he hasn't retired. His is a cautionary tale that, regardless of its super-sized scale, has much to teach. Only Redstone may know why he keeps on, even at the expense of his most precious relationships.

For one, Redstone gives a window into how close friendships and familial relationships diverge in (what should be) retirement. You choose your friends and associates, but your family, not so much. So while Freston and Cruise have likely moved on, Shari doesn't have that option. That's unhealthy all around, and saddest for Redstone himself.

A guy like Redstone, who built a fortune estimated at $9 billion, may have made one hell of a mentor during his transition into retirement, and perhaps in retirement itself. There are so many options left unplumbed.

Work can and should continue to be part of life for retirees for whom it balances a healthy portfolio of interests and activities, and serves as a prime source of mental challenge, a feeling of social connectedness and other vital things. There's just no glory seemingly vowing to die in your head-of-the-boardroom chair, simply because you can.

Michael Burnham is CEO of My Next Phase, a consulting firm offering non-financial retirement planning products and services (www.mynextphase.com).