-If I have been in jobs for long periods of time, I would stress that when a restaurant is the right fit, I like to build a base of repeat clientele & that I'm usually the go-to guy for questions from the guests & staff. If most of the recent jobs I was at was under year, I'd stress that initially I thought that it was the cultures in the individual restaurants, but then I discovered that it was that I've grown tired of the stale atmosphere that casual dining provides. I'd follow that up with stating that I'm interested bringing my skills to a new arena, especially with an constantly evolving menu (they'll usually have 2-6 daily specials) that keeps the staff sharp.
-When asked why I'm looking for a change (as in a different type of restaurant, I'd say something like "I was talking to a friend/cousin who works in a _-Star Restaurant (in a far away state if asked) & we were talking shop. While I was griping about unreliable, 20-something coworkers who are just working for beer & gas money or corporate micro-management, his gripes were that they ran out of the Macadamia Crusted Mahi-Mahi before he could order it for himself & that he'd gotten something on his favorite tie."
-At 40 I wouldn't mention my age. They'll know you're older by your appearance (which is usually what they're looking for, for more reliability, accountability, etc), but when you state your age they may start to question why you haven't gone into management "at your age".