If exercise is your top reason for getting a bike, I'd suggest a regular trike. They handle differently to a bike but you get used to them. They're easy to mount and dismount. If you opt for an electric bike or trike I'd suggest get one from a bike shop, not a big box store. It will cost a bit more, then when it comes to servicing the machine, you can rely on the bike shop but you won't get any service from a big box store. A bike shop might not want to service a cheap bike or trike, as I found out when I took a friend's trike to a bike shop. The freewheel had gone bad and they said they don't service trikes. And this was a huge bike shop with two stores! I ended up doing the repair, myself.
One other consideration is where you will be riding. If you have safe roads in your area, then you'll be in good shape, but if you have to transport it, a trike will need a pickup truck or small trailer to tow it. I'm 76 and although e-bikes look interesting, I ride for exercise so my pedal bikes are good for me.
