My first time nude in public was at the beach in Brighton way back in the 1980's when I was late teens/early twenties. I came down from Newcastle and it felt just so great to be as nature intended. I did get a few butterflies when walking along and wondering if I would be able to do it but seeing a few people there nude it felt rude not to follow suit. Took a dip in the water too.
Since then I've never looked back and always look to get nude on the beach. Living in Asia now it is not so easy but where there is a will (or a beach) there is a way.
My first time as an adult was skinny dipping in the river with my mates. We'd go to a safe enough spot , strip off and jump in and muck about as bunch of young blokes would. We tried to entice the girls in... of course, but they stayed clothed and dry on the river bank wtaching patiently as we showed off!
It was a different time but this was quite normal when I was a lad in the mid 60s. A group of lads, and sometimes lasses, would go out together and would often strip off and swim in rivers and lakes. Swimming trunks were made by your mum from wool so pretty useless so no one bothered. I think these experiences in childhood is why there are so many "white old men" are naturists.