I care more about my health and long term well being than my company and the code I write. Walking 5 min every 30min won't kill your productivity, it might have the opposite effect actually.

I started exercising when I saw that most of my older peers in the field were fat/obese, had poor posture and no stamina whatsoever, these people are literally rotting day by day sitting in front of a computer

It seems so insane to me that some people internalised the idea that companies and productivity are the #1 priority in life, I can't even begin to wrap my head around that. As if selling your time wasn't enough, now you have to sell your body. Unless you live in some weird hellhole of a country without mandatory rest breaks laws I don't see why you would put yourself through sitting more than a few hours at once