Two years ago, at the age of 48, I was unhappy with my weight and conditioning. So, I went back to the gym (boxing), trained hard and managed to get down to an over-lean 175 lbs. Of course that took working up to 40 rounds of heavy bag work (that's two continuous hours, no breaks or rests permitted) three days a week, and a great deal of speed and double end bag work in between. Stuck to the bicycle instead of road work, these old knees don't enjoy the pounding. Did some limited sparring, but my gym is not very willing to have old farts like me taking punches, and the utter lack of other boxers even close to my age makes finding a partner very difficult. Probably for the best as my wife claims that I already have enough brain damage.... I can't remember why she thinks that though.....
I still hit the gym 2-3 times a week, and I'm holding at 181 lbs.
Typically, if one sits in front of a computer all day, one will gain weight and lose conditioning. Besides a good workout will improve one's alertness and consequently only serve to improve their game skills, IMHO.
Boxing is a great sport for conditioning and weight control. Just find a good gym and a trainer willing to work with someone who has no interest in competition. Moreover, like any martial art, the skills you develop may come in handy someday, although that's the last reason to go to a gym or take any course in martial arts.
My regards,
Widewing