I was 42. I just got a job teaching at a school in my hometown and I was running shirtless as I often did and some students saw me. It was all over school the next day- thank God there was no social media back then.
Now, I was told that I COULD run shirtless by a woman I was dating (she's 25 years younger than I am) but my view is:
At a certain age there are two reactions:
1. Ewwww old man put on a shirt.
or
2. Look at that old man trying to show off his body.
So, I wear a shirt.
By the way- for all the down votes- this is a true story. There are guys my age who go shirtless. Some should and some shouldn't. It's up to the individual to be comfortable.