Leg and core strength as we approach ages where muscle mass is in decline remain as important as cardio health.

Skip upper body if you want but skipping leg, back, and core days is done at your own risk.

At least do walking lunges a few times a week. Or squats once a week. They suck! But not being able to do them as you grow older is worse.

(I'm your age too, and am also trying to balance weight work with riding)