I'm 77 yrs. old, have been riding for 61 years, and plan to keep riding until I'm 80 if my health holds out. I had a bypass in 1994 and two stents in '08. In July of '08 my wife and I rode with two other couples to Anchorage , Alaska and back. It took a month and was 9264 miles.
I am only 67, and just got a new Limited cause my '06 Ultra had 93,000 trouble free miles. Also have a Nightster that I race at Bonneville each August. This summer will be hectic; so many trips planned and so little time.
I'm 58. The way I look at things, I will continue to ride as long I'm healthy and alert enough to not be a danger to myself, or others. How will I know when 'enough's enough'? It's a tricky question, probably because the deterioration of reflexes and health progress at a such a slow rate in the usual case, you don't notice the 'scenery' passing by you. Just something happens to you one day, causes you to look up, and when you do you notice certain things have passed you by. That is, if you're lucky, it'll happen this way, i.e., you'll survive to have the epiphany.
This is a good question. How will I know when I'm done? It deserves a definitive answer...and I don't have one.