This off season, and frankly for a year, I have tried to walk more. My wife is a big walker and she & I often share our strolls. For the past 6 months I have averaged 4.1 miles a day. I thought I was ready this Spring for walking a course for 18 holes but it turns out, there is a big difference between 4.1 miles and a walking round of golf. Today's round was 5.2 miles. Plus I was pushing a golf bag laden cart. My legs start getting fatigued around the 13th hole. It is not like I can't play. Rather, I have to be aware that I am getting a bit tired or my swing goes to poop.
Now that I am somewhat regularly playing/walking 18, maybe my body will get used to the extra demands. At least that is my hope.
I think that those of use in the northern part of the country suffer from the same thing. I also try and walk during the day in the winter but it's not the same as walking the course and pushing a cart. I getting to be like a bear and put on some winter fat as well, despite trying not too. However, I know that I'll get the stamina back and lose the weight once I start working outside again for my job and playing.
I am eternally going to recommend weight exercises, even if just lower intensity stuff using dumbbell, such as lunge and goblet squat.
Mainly say that because walking for exercise requires so much walking and time, which is getting harder and harder to come by. One of my neighbors walks for exercise and he is constantly out there. He says whenever he indulges in a bacon cheeseburger or something, he'll have to pack on even more steps the next day. I just don't like to see that. Even 30 minutes of a vigorous weight workout probably does more for a body than a couple hours of walking. And in a higher intensity work out with weights, that's not even a steady 30 minutes of activity. A lot of that time is dedicated to resting between sets, time with which you can lollygag and do whatever you want. I look at my phone and do crosswords.
With golf it's not just the walking but the standing for 4 hours that gets you. I do a lot of walking outside of golf (running is tough on my back), so I don't think physical fatigue is an issue. I just do stupid things after a few holes.