I guess this is aimed more at older devs and admins who have been sitting at their computers for the last 20 years like me.
I'm starting to feel my age. I get tired quicker. My health isn't what it used to be. I get the feeling that staring at a computer screen and sitting down all day in an office is not particularly healthy.
Has anyone got any tips how to improve mental and physical well-being?
Sleep is something which is seriously overlooked in general. From personal experience, getting enough sleep and eating well are requirements that need to be met first before exercise.
There is nothing is worse than exercising whilst you are deprived of sleep and mal-nourished.
Speaking about exercise, don't get hung up on dogmas and "this is the only way" personality that is common in the fitness industry. Pick what works for you. Just make sure you are moving on a daily basis because sitting down 8 hours everyday is not healthy at all.
Go for long walks in the park with family or friends. As silly as it sounds, it works. Walking is not only good for you physically, but also psychologically [0]. Walking is a basic human movement pattern and is one of the first things we learn how to do early in our lives.
My grandfather passed away at 94 two years ago from old age. He never went to the gym, never participated in long marathons and he was a frequent beer drinker. But he did long walks everyday on the farm in the morning and evenings, he also ate well and by 10pm he was in bed.
Morale of the story is that, go back to the basics and stick to them. You won't go wrong.
Edit: Added a reference.
[0] http://news.stanford.edu/news/2014/april/walking-vs-sitting-...