I just got the new Nashbar catalogue, which appears to
be pushing fixed gear bikes as the hot new technology.

=v= They're about 10 years late to the party, but hey.

=v= Fixies are fun, they're just very a different feel. Your
legs have a direct connection to the bike and never stop moving,
which means you can't coast, and you use your leg muscles to
pedal backwards when stopping. A classic fixie setup is to
have a rear wheel with a different-sized gear on each side of
the hub, and you can flip sides for mountainous terrain.

=v= Fixies have a minimalist beauty and some people take it
further by not having any brakes. The result is a "track bike,"
so named because it's intended for riding on velodrome tracks.
One stops, as I mentioned, by pedaling backwards.

=v= Track bikes aren't street-legal (there are laws requiring
brakes), but some people do ride track bikes on the street.
There has been much fear and panic about this, as if there's
been a sudden influx of insane bikers who can only stop by
crashing into widows and orphans.

"I still feel that varable gears are only for people over
forty-five."
As I mentioned, I'm 46, so that answers PART of my question!

=v= As you can imagine, fixies put more demands on muscles
and joints (especially knees), as would any single-speed bike.
My friend Jon is 50 and has no trouble riding his fixie every
day, and he lives in a decidedly unflat part of San Francisco.
_Jym_