No seriously though the other reason 35-year-olds buy a motorcycle or convertible or similar pleasure vehicle is that they actually can afford it, unlike new grads just out of school? (I differentiate the pleasure vehicle from the utility vehicle; if you buy a little 125cc motorcycle as a car-alternative for zooming around town that's quite different than the speed machines, or the massive touring motorcycles that get SUV-grade gas mileage.)
Anyway, this is one of the positive parts of middle age — maybe you're not actually rich, but you're usually much better off then you were in your twenties, might have a good start on a home or a retirement, and can afford a few personal luxuries, or children.
The "(hopefully)" is interesting! Living in an Arabic country and having many Mediterranean colleagues I recently started to appreciate that different cultures have a very different point of view on when kids should leave their parents house. For them it is perfectly normal to stay with their parents until the age of 25-30, while e.g. in Germany this would be considered quite weird already.
Narrator: "And his life just got shorter"
It sure sounds like it. Regarding "buying a Harley" I think that can act as a shorthand for "realizing life is short and doing something for yourself now that you have the means and while you can enjoy it", which is a good idea in my opinion.