I'm not sure if LGBT rights is an example or a counterexample for this phenomenon. A lot of countries made huge strides in that area in the last 0-3 decades, which wouldn't have happened if nothing about all the old people (which are overwhelmingly in power) changed, especially because over the same period politicians became older (so the age cohort in power stayed roughly the same in lots of places). However, when you do look at polls by age group it seems to me like the changes in old adults are rather modest, while young people overwhelmingly support.