Last summer rode maybe a dozen times starting at 8,800' and ended up at 9,500' where I had to stop every time. At 78 what can I do to condition myself and do better this summer?

You're up in the bracket where doing a lot of VO2max intervals is contraindicated. Your fitness is very good and you obviously know how to manage it. That leaves supplements, which do work. Take a look at this: Mountain Might, Altitude Training, High Altitude Training
I have not used their stuff, but it gave me the idea of looking into similar supplements.

For an equivocal review see: https://www.bikeforums.net/18019606-post33.html

I have had good experiences at altitude taking for about a month before an event:
n-acetyl cysteine, 2 X 600mg/day
acetyl L-carnitine, 2 X 500mg/day
alpha lipoic acid, 2 X 250mg/day
sublingual B12, 1 X 500mcg/day

I've also used the sodium phosphate as in Mountain Might in a 4 day loading program with good results:
Race Day Boost - Increase Athletic Performance | Hammer Nutrition

When going up quickly to altitude, I've had good results from over-nighting at altitude before the event.

Some years back a friend who used to compete, told me the tale of some former team mates who were hired by a film crew to do some cycling in one of the local mtn canyons to create some footage to accompany a news story. What they did not learn until the story hit the air, was that the topic was an off-label use for a common prescription drug.

https://www.sciencedaily.com/release...0624120556.htm

Acclimitizing to altitude takes time, more for some people than for others. Take whatever amount of time your body requires. To ignore the process risks health consequences. OA Guide to High Altitude: Acclimatization and Illnesses