Is he swallowing a lot? Does he have a trace of a heart murmer? My cat Jake had the same thing - here's the thread I started: http://www.pets.ca/forum/showthread.php?t=46076
Turns out he had a Feline Herpes outbreak that was misdiagnosed. Usually asthma doesn't develop in older cats, but it can't be completely ruled out..
Has Tommie been in a slightly stressful situation lately? Many cats have FHV but it's dormant until they experience something stressful - a move, a new cat, a new family member, that sort of thing..
You can't cure it, but you can treat it. I had Jake on some Clavamox and some L-Lysine, and he was better after a short while.
Good luck and keep us posted!