This just means you felt older younger. Feeling old is in comparison with yourself if you have improved upon your life style in some form or fashion since you were younger that’s a kudos to you. But if everything was all on a level playing field you should of felt better at 31 than you do now.
Didn't want to derail the thread, but when I was 31 I weighed a lot more. I used to wake up in the middle of the night choking from sleep apnea.
All it took was just the slightest bit of effort to exercise when I was 36/37, and 50 pounds immediately dropped off.
Plus, that was back when I thought I could get rich off of penny stocks pumped up on message boards

.