Rich,
Do you think declining vision may have something to do with that? I'm starting to wonder if my putting woes aren't vision related.
Mike,
Speaking only for myself, I have no doubt that aging eyes have impacted putting, and on multiple levels. I don't think I read greens nearly as well anymore (and I was never especially good at it!); the subtleties of a green just aren't as apparent. Equally importantly, I think my peripheral vision has declined at least marginally as well. And, at the risk of getting REALLY geeky, I think the degree of what is known as parallax error has increased; this may be related to the peripheral vision decline as well.
To that end, in the summer of 2015 I decided to try face on/side saddle putting for one year just to "see" if it would make a difference. (I based the one year window on something Randy Haag wrote on his blog; he's one of the better senior ams in the world, and has putted this way for many years now.) About three months in, I got rid of every conventional putter I owned except for a Ping with sentimental value and a Scotty that I knew I couldn't get my money out of; I knew I was never going back. There is just a ton I do NOT know about golf, but I have no doubt that this is a better way to putt a golf ball for several reasons, not the least of which is putting with binocular vision just as you lined the ball up, instead of trying to move to the side and tilt your head.
Rich, as to the zone:
I would think that the zone would still be available if you are playing competitively, though the results probably aren't as magical as when we are young and strong and flexible. For me, the zone is MUCH harder to find when I just play casual golf, likely because my mental abilities have declined along with the physical ones. Competition and playing make-believe seems to help that, but that might just be me.