Walking is the best exercise you can do and you can do it your entire life.
I would add in some walking WITH DUMBELLS also. Not heavy, light enough to enable arm movements for power walking.
Cycling is amazing and freeing once you get past the fear of exposure. It carries more risk if one falls, though. A comfortable, proper saddle and stable bike are musts (I use a sturdy touring bike, the Surly Long Haul Trucker...which to me would be perfect for older folks...think Cadillac heavy and comfortable).
Unless you have a bad back and you can’t walk very far then what? I loved to walk and did so every day then hurt my back. Can’t walk or stand for long.