First time nude in public? That's a good question. So young that I can't remember. My maternal grand-parents were practical and frugal, and that set the attitude towards clothing. Don't get your clothes dirty. "If you're going to play in the mud, take your clothes off."
As a child, I had a vitamin D deficiency, and there were two solutions, cod liver oil (yuk) and more sunshine. Since sunshine was free and my parents didn't have to force me to take it, playing nude was the solution.
Being raised in the rural Lower Mainland of BC, most of it was rural then, exploring (hiking) with your playmates (boys and girls) was the common activity (no sports fields), if you got too warm, you went skinny-dipping in the next creek, no big deal.
As a child I didn't have a bathing suit or a tuxedo. "Why buy something that you'll hardly ever use?" Going to the beach was a special event, maybe twice a year, and when we did, it was to one end of the beach. Mother had a bathing suit (the only one in the family). Dad went in the water in his underwear. Granny brought a second house-dress to wear in the water. Grandpa, my brother and myself went in the water nude but dressed on the beach.
Would you believe that my family was very religious at this time? They were, but "modest attire" meant don't flaunt your wealth, not hide what God created, your body. When I was a teenager/young adult there were a lot of places in the Lower Mainland that we would go to and party and skinny dip, but most of them have become regional parks now. My first wife didn't have a problem with nudity, she would strip anytime and anywhere. I was too conservative.
When I was dating my second wife, Germaine, I in invited her to Wreck Beach. The response was "I'll go, but I'm wearing a bathing suit." While chasing one of my sons, she fell out of her top, and off it came. About 10 minutes later, "What the hell." and off came the rest. The following year the climb/hike became a problem for Germaine, so we looked for a nudist club. We found and joined the old Sunny Trails Club in Surrey, and have been part of organized nudism ever since.
We are probably not true Nudists/ Naturists because we actually believe that nakedness is natural and not sexual. They really don't, or there won't be so many rules to prove that it isn't. Don't do this or that, or don't wear this or that, because it might appear to be sexual. More on this at an other time.