Sore knees

Leg strengthening exercises.... squats, leg presses and the like.

Have you been to an ortho to rule out arthritis? Get you a good PT and get some exercises specifically for you.

I started out with an achy left knee after walking/jogging...

years of steroid shots and gel injections later... finally getting that bitch replaced.

My ortho did tell me he has one patient that's 100% bone on bone... never had it replaced... runs 2 marathons a year and does some sort of ultra mountain running thing as well. While bone on bone. I don't see how it does it... but whatever.

Yep, it definitely sucks too.
But me being fat and out of shape sucks more. ??
Looking back through my log books, when I was doing deadlifts my legs felt stronger and my knees didn't hurt post run as much. In preparing for this latest half marathon I was reluctant to take an extra day or two to include and then recover from the deadlift sessions. Probably should have bitten the bullet early on and included them.

I'm 53 and starting running again after a long layoff due to my health. I'm also at least 30 pounds heavier than I want to be.

I use a joint supplement called Chondroitin & Glucosamine, along with Turmeric. It has been a life saver for me for inflammation after a run. I don't know if this is the same issue you have been having, but it was a game changer for me. I have zero issues with my joints now.

* If you go this route, make sure to get the turmeric with black pepper for better absorption. It is a little more expensive, but worth it.

You need to get used to being on a bike if you want to have good mobility throughout your 70s. Also, at your age, resistance training is so important. 90 min runs are a bit much