I doubt this is the reason. Guys born in the 70's and even more so guys born in the 80's are more modest around other guys than any generation that I have witnessed myself. I can remember back to being around men born in the 1890's to the present.

I suspect that as humans continue to grow in height that the average length of the penis is also going to grow though not at that high of a rate.

I suspect that it is just coincidence in your case. Or having gay tendencies you are now more open to younger adult men than you were when you were that age.

Guys born in the 80's, now ages 18-28, are a bit young for me to know the answer to your question from a sexual point. My sons are in that age group. They are more open to walking around in their underwear in front of just about most anybody than I was at that age. But they don't walk around in the nude. Bathroom time is a privarte time for my sons.