Join Date: Jan 2009
Location: Vulcan, Michigan
Poor conditioning will tend to show up more after you've shot a round or two of clays.
Are you shooting with a gun that's new to you? Maybe it doesn't fit. Or maybe you don't fit your old gun anymore. What I mean is are your cheeks "fuller" than they used to be? You may need a little castoff in the stock now so your eye aligns straight down the barrel.
None of us shoot quite as good as we did when younger. Natural part of aging - reflexes aren't as fast, eyesight isn't quite as sharp or able to track moving objects quite as good, muscles don't have the tone they once did, etc. But, barring some medical problem, the drop off in ability shouldn't be too extreme.
Good conditioning, even for young guys, will help. An eye exam may be a good idea if you haven't had one recently.
And you didn't say if you've kept shooting for the past 40 years or took a hiatus from it. If you haven't shot much for 40 years it will take a while to regain some of that skill.
If you're consistently shooting left of the target the first thing I'd suspect is gun fit, regardless of age.