Yesterday, I was stopped at the traffic lights near $college. A Mk 1 Young Person crossed the road in front of me, paused halfway, picked up an empty plastic bottle that was rolling around in the breeze, and continued to exit stage right.
I don't think I've ever seen a young person spontaneously pick up litter that wasn't their own like that. Older people do it from time to time, usually near their houses (this is probably a demographic thing, as older people tend to have more stable housing). Younger people's wombling tends to be an organised affair with binbags and litter pickers.