When I was 20 I was 175lbs which was slightly underweight 2 weeks ago I was an all time high of 233. I went from working hard to working in an office my diet stayed the same and I barely excercise (except sex). Im trying now to lose weight and hope to start an excercise program. I did do taekwondo for the last few years and that helped some but I quit.
You have likely had an increase in intra-abdominal fat. It is very common as we age. Stress can play a big role in it.
Waist circumference is probably the best thing that you can keep an eye on.
Taken from my waist circumference measurer - <37" GREEN (fine/healthy), 37-40" ORANGE (take measures/try to reduce), 40"> RED = Problem & increased risk
You take the measurement whilst not sucking in your stomach, midway between the lowest rib & the top part of your hip (iliac crest). Waist /height ratio is another alternative to this, that some people prefer. However, I think someone has to be of truly exceptional height for the above to be scewed.