Okay - so I know I'm getting old but...

I did a 90 minute Spinervals tape this morning and now 4 hours later I can really feel my knees. No problems during the workout. I know I was keeping my cadence up even when pushing the big gears. Two of my older sisters have arthritic knees so I suppose it may be inevitable, but I don't want my knees to keep me from pushing hard. Anyone else dealing with knee issues?