Is loss of breath capacity something that just happens as you get older, or is there anything you can do to prevent it.
Specifically, does anyone know of any web sites or exercises that might help regain, or at least retain, breath function?
Google “breath builder”.
It was recommended to me by a professional flutist as something she recomments to her students, to help them improve their lung capacity. I got one, and my roommate says it’s similar in design & principle to the device that she was given in the hospital after chest surgery, for the same purpose. I got it because I was a smoker for years and that really did a number on my lungs.
I should get mine back out, actually. I put it away during some pre-houseguest cleanup hysteria (ack, Mom coming to visit!! must appear clivilized!), and hadn’t unpacked it yet.
There are also some good web sites out there with breathing exercises. Unfortunately i lost that bookmarks file when my last computer died. Anyone else have links to them?
breathing capacity usually declines rapidly at death. I got one of those breathing contraptions after my heart surgery. It worked. I also got a harmonica after my heart surgery. That’ll build up lung capacity like nobody’s business. It’s way more fun. Plus, you learn one more instrument. There are free lessons on line and a cheap harmonica costs $5 at your local guitar store. A person can judge their breathing capabilities by how long they can hold those notes. The basics of a harmonica can be figured out in one hour. Keep one in your pocket, car, and whereever.
This is a point not to be overlooked. 
I recall the story of a very old gentlemen being asked how he lived so long. “Keep breathing.”
There is also a marked tendency to switch to playing instruments with many strings. Do you think the two are linked?
Yes, and fingernails keep growing after death, so plucking is (super)natural.
My favourite breathing exercise is to take a deep breath and exhale slowly whilst saying “pint of bitter” as many times as possible. Caution: don’t try this exercise in a pub.
Actually playing a wind instrument is the perfect breathing exercice in and out of itself.
During normal respiration, inspiration is actively caused by contraction of the diaphragm, while expiration is mostly a passive act following the relaxation of the muscles. When the pressure in the lungs surpasses the pressure in our surroundings, the air is being exhaled.
With age, the elasticity or compliance of the body’s different tissues lessens. Respiration becomes more shallow and especially when lying on our backs, the alveoli (smallest parts of the lung where the actual gas exchange takes place) in bottom parts of the lung collapse. This is called atelectasis.
When you take up your whistle or any other wind instrument, you immitate what people suffering from a chronic pulmonary disease often do to ameliorate their breathing: you augment the resistance of your airways. This means that you have to exhale against a higher pressure than normal.
You can feel your body’s reaction to this augmented resistance: Exspiration is now an active action, for the diaphragm and various other muscles contract to press out the air from your lungs. → Muscle training
Then there’s the positive pressure issue. During normal expiration, the pressure in your lungs lessens quite a bit to the point where some of the alveoli collapse. When playing the wind instrument, you still have a positive pressure in your lungs at the end of exspiration (PEEP). This helps to open up the collapsed alveoli and helps to keep them open.
In the end, there’s only one thing to be said: If you feel your breathing is getting shorter for no apparent reason and you feel less fit, do consult a physician!
Tikva
Stop it at once!
Don’t you listen to him! Just you go on breathing as much as you want!
GASP
wow…that was close
But you’re steaming up the windows! D’you want us to crash and die?
Pint of bitter, pint of bitter, pint of bitter…
Long walks, bicycle rides, lap swimming and other aerobic activity
are a good way to preserve breath function as one gets older.
the switchbacks up to White Pass (the white pass just south of Glacier Peak)
or the trail to Blanca Lake
oh no!!! not that!!! 
Just when you thought this thead had expired…
Actually, contrary to popular belief, in the kingdom of heaven there will be wind instruments also (check out Psalm 150). I have a gold Irish whistle waiting for me in heaven. I will there have the ears to play without earplugs, and the whistle itself will be sweet, pure, and not any louder in the high range than in the low.
Praise Jesus!
gonna need more cowbell…
Dream on, as the “angel” said to the ?virgin(s). 
Has heaven got different acoustical laws, then? 
You could even have an Irish gold one, apparently, these days, since they discovered (or rediscovered) said nefarious substance somewhere in Monaghan…