Based on personal experience as one of the older forum "regulars," (I'll be turning 63 next month), I still have some sweaters giving good service that my mother knit for me while I was in prep school. As to shoe size and waist size increasing, I had both occur during my 40s: Since the time I had been 15, I took a 13C or sometimes a 13B shoe. During my 40s I went up to a 13D (which is nice because D width is generally more available). As to waist size, from the time I was 22 to about 45 I was normally 36, then rather suddenly went up to a 38 and continue to wear a size 38 although depending on the cut, they can be rather loose. I think I am actually about a size 37. I did a lot of running and worked out a lot with weights for many years. Since I blew out a knee about 8 years ago, I haven't been able to run any distance without aggravating it, and my primary exercise has been walking my dogs--usually three to four miles on working days, sometimes much more than that on weekends. I like to think I'm in pretty good shape for an old buzzard...or maybe I'm just deluding myself.
In brief, if you stay in reasonable shape and don't overeat, there shouldn't be too much change. I would however counsel against undertaking a vigorous bodybuilding regimen AFTER you have accumulated a wardrobe of good suits. (I made that mistake after inheriting about a dozen really high grade suits from a rich relative who had passed away--one of my many youthful follies.)