I think around the the age of 9-10 years old was the last time I was made to strip completely naked whilst changing at the beach.
As I got older I would just take off my trousers then wrap a towel around my waist remove my underwear and put on the swimming shorts that's what I normally do when changing at the beach or swimming pool... That's also the way I have seen most people male and female change clothes on beaches in UK, strip down to there underwear and then cover themselves with a towel whilst changing from underwear to swimwear.
I can remember one time some old people casually got changed at a beach and got completely naked... It was a very secluded beach the type you had to walk to so not loads of people about and I didn't really have interest in seeing naked old people
Iv seen plenty of people male and female in there underwear at the beach before changing clothes or going I to the sea, happy to share if anyone's interested?
I often go swimming, it has an open changing rooms the majority of guys change in the open without anything to cover themselves age doesn't seem to make much difference.
For years I would strip down to my pants/briefs then cover myself with a towel but recently providing the changing rooms are not too busy I will change without anything to cover myself. I have been caught naked a few times but after the first time I wasn't that bothered.