I would like to know what the life expectancy is for those who
regularly ride motorcycles between the ages of 18 and 35.

There are about 10 motorcycle deaths per million hours of motorcycle
riding.  The average motorcyclist rides maybe 100 hours per year,
which equates to about a 1/1000 chance of death each year.  I'd guess
that that knocks a couple of years off life expectancy.

Wouldn't that be 1 in 10,000 by that calculation?

No.

Rracecarr, you're right, of course.  Sorry for having questioned your work.
(Darn, I saw the 10 per million hours ...  :-(
Myoarin

I answered a question last fall for someone interested in motorcycle
safety statistics. Unfortunately, it seems the entire
question-and-answer have disappeared altogether, as the number appears
to have been reassigned. However, there were some references in that
answer that I think you might find interesting, and I've found a
cached version of the question (for now) here:
http://72.14.203.104/search?q=cache:uhAws0oIG7sJ:www.google.es/answers/threadview%3Fid%3D433481+motorcycle+statistics+byrd-ga&hl=en&gl=us&ct=clnk&cd=1

I found this:

What are the odds of dying?
http://www.nsc.org/lrs/statinfo/odds.htm
..."Odds of Death Due to Injury, United States, 2002

Motorcycle rider (V20-V29):

Deaths: 3,215 
One Year Odds: 1 in 89,562 
Lifetime Odds: 1 in 1,159 

One year odds are approximated by dividing the 2002 population
(287,941,220) by the number of deaths. Lifetime odds are approximated
by dividing the one-year odds by the life expectancy of a person born
in 2002 (77.3 years)..."

Although this isn't directly answering the posted question, I thought
I'd add some comments on motorcycle fatality statistics. To be clear
up front, I have been a motorcycle rider for over 40 years. I *always*
wear a helmet and have never [knock wood] have had a serious accident
on a road motorcycle, but have had a couple of pretty bad spills on
dirt bikes that involved concussions, fractured helmets, stitches, and
visits to an ER.

So here are two questions to ponder: 

1) Do you think wearing a helmet will improve your odds of surviving
in a motorcycle accident?

2) Why do 7% of the states account for nearly half of all motorcycle fatalities?

Answer 1) Based on USA nationwide street motorcycle crash data, the
fatality rate in single vehicle crashes (just a motorcycle involved)
is not statistically different between wearing and not wearing a
helmet. When you combine fatality rates for both single and multiple
vehicle crashes (i.e. motorcycle and some other vehicle), the fatality
rate is actually HIGHER (statistically significant) WITH helmets than
without!

Answer 2) The seven most populous states in the US make up almost half
the nation?s population. The fatality rate in these seven states is
actually very proportional to their portion of the total population.

I found this out in researching certain "statistical myths" for a
paper in a business statistics class last summer as part of an MBA
program. Although these facts could be used by those that advocate
against helmet use, my conclusion was that if a motorcycle accident is
bad enough to be fatal, wearing a helmet will not make the difference
between life and death. Kind of sobering when I came to that
conclusion. Two other major factors in motorcycle fatalities: being
drunk, and speed as causes of the accident both of which are about
twice as frequent in motorcycle accidents compared to car and truck
accidents.

My personal bottom line: a helmet isn?t going to save you in a bad
crash as it's the internal injuries that get you. But I am sure a
helmet can make the difference a concussion and  "vegetable" in a
non-fatal accident. And definitely don't drink and ride (or speed for
that matter).