For some inexplicable and totally illogical reason, I don't mind seeing a young person in a Bikini at the beach but someone my age needs to be more mindful what we subject other people to. I like to blend in - I know some like to stand out - so I would not be in a bikini at the beach or anywhere else.
However, many moons ago, we ran around the beach in Italy in bikinis and nobody thought anything of it - without kids and the potentially detrimental effect they can have on clothing that can be easily "dislocated."