Hmmmm, tough question...
About 4 1/2 yrs ago, I was diagnosed with gynecomastia. I, personally noticed something amiss then. My nipples were always excited, and my little areola's had developed what I would call "platforms".
They were mostly soft and squishy, but had a stringy, but tender core.
But, for them to be noticed by other's, I would have to say about a year and a half ago. My wife noticed that I was rubbing them when sitting watching tv and such. She said if I kept doing that, they would only get more sore and larger. LOL
About a week later she suggested we go shopping and that is when she picked out my first camisole thinking it would cut down on chaffing, and a couple of Athletic Bra type of things. She thought the compression might keep them in check from being noticed and make them feel better..
I very rarely ran shirtless in the past, so that much hasn't changed except I KNOW they are getting tougher to hide and have decided not to be obvious with them, but not hide them anymore.