I am 15 years into this game, 100% trad. I will turn 50 in 6 weeks time, and feel as fit as the day I started (well, fitter really).
I believe the reasons are that I always take my time, and have a relaxed attitude towards my work (although I am OCD-ish regarding attention to detail).
I don't smoke, I drink very occasionally, I have never seen the inside of a gym all my adult life, and I don't exercise.
I am 5 feet 10 and weigh around 12 stone (the last time I checked was 11 months ago when I was about to undergo a hernia op).
My work hours are from around 9:30 to 5:30 (longer in summer) and I work most Saturday afternoons.
I don't feel your pain literally, but I empathize with you.
John