My grandfather continued to breed horses until he was 87. He didn't make a decision to stop, he simply had a stroke and has been restricted to a wheelchair.

Now he's 94 and he avidly reads books in English, German and Danish. He's trying to learn about the internet, but hasn't really gotten down the concept of "surfing the web".

Yes, you can be productive past your 80s. I plan to be, but I also have six decades until I'm there.