I'm 34. I've always had a problem with shirts not fitting since I'm 6'-1" and feel like i have a long torso. I'm around 200lbs. I lifted weights a lot and now I'm cutting. My stomach is getting flat, but i'm still wide. I always had broad shoulders, maybe my waist is widening up for that.
When I was younger, I always felt I was odd shaped. Like a "V", and I didn't have huge muscles.
So, i do think it might be part of the aging. Or you might be getting fatter.