I’m retired as well. We are fortunate enough to have a bike path very near to us.
I have been walking and have extended the distance I walk to 6 miles round trip.
I’ve been thinking of getting a bicycle, maybe next spring, and extending my range. My brother just turned 70 and he and my sister-in-law take their grandkids out now and then.
Maybe next year will be the year for me..
That said, the only thing about walking is that unless you are walking in the hills and mountains, it isn't much of a cardio workout (no heavy breathing/heart pounding)
A bike on the other hand will turn your heart into a beast because it just gets stronger and stronger.
I have a good friend who had a heart attack (a widow-maker) several years ago. After he left the hospital, he started walking. He then got a bike and started riding every day.
That's been a few years now and he is still riding between 5 and 40 miles a day.
He's one of the guys I ride with.
In fact, he's the fastest of the old-timers I ride with (he's now 74 and in great shape).
BTW, he didn't get fast intentionally. He just rides a lot and all of a sudden he discovered he was faster than everyone else...usually without even trying.
Cycling is very popular with old-timers because it's easy on the feet and legs. There are many clubs for old-timers. Needless to say, they are a handsome bunch of men and women.;-)