Interesting question. Personally, I do not believe that the elderly in Japan set trends for anyone else than members in their own age bracket. I have to think about the whole hair-dyeing thing: purple hair is seen fairly commonly with elderly Japanese women, but does not descend to other age brackets; moreover, henna dying, while popular with both sexes, seems restricted to people in and around their 50s.
As for travel, and the latest push toward volunteering overseas: again, I do not see this as setting much of a trend for younger people, as much as it is a way viewed by older people to spend their time and money in a constructive way. If anything, younger Japanese have ventured with more frequency outside their nation’s borders, so it would suggest to me that older people are taking the cue from them.