Why whistle ye not?

Why is that nobody under the age of about 35 ever whistles? Not just here in Italy, but also in the UK. It’s very odd to me; personally I don’t even realise that I’m doing it.  The other day, coming out my radiotherapy, one of the other guys said: ‘How come you’re not whistling today?’ It transpires that every time I come out I whistle . . . relief, probably.

Anyway, anybody got any theories? ideas?