What is a 'generation' these days?

I know precisely what a generation is in biology, say in bacteria cultures or drosophila experiments. I know what it means in chemical and physical iterative, enumerated events, done in a lab under controlled circumstances. In science everything is precise, or tries its damnedest to be, and I understand the concept of generations very clearly.

But what about the popular idea of "my generation" or "the younger generation" or "the generation gap" or "my parent's generation"? Most people know that (at least in so-called Western countries), giving birth to children has become an event that has migrated to a later and later period in life. Through most of history, and presumably in pre-history, women gave birth nearly as soon as they reached puberty, and continued to do so for most of the middle part of their lives. So a "generation" could be held up as something like 15-20 years, the age they were when they first gave birth to another "gene machine." In fact, 20-25 years even now seems to be what most people have in mind when they talk about the World War II Generation, The 60s Generation, Generation X, and now Generation Y.

But does this really make sense? In the developing world, sure - though I'm not sure how concerned they are with concepts like 'generational culture drift' - not to sound smug about it, but they're mostly just trying to grow food, eat, and not die of disease or starvation or natural disasters. Amongst more prosperous nations though, it's hard to call 20-25 years a generation anymore; if women are regularly holding off giving birth until their mid-thirties, then that figure is the generational turnover. It may seem a pedantic point (to sneak a word in), but it really isn't. Insofar as children are taught the basics in life by their parents, the generational turnover really has slowed into the mid 30s in a real sense.

But at the same time, one would be hard-pressed to argue that 'cultural drift' has slowed its pace. It hasn't, of course; perversely, it's ramped up to dizzying speeds thanks to the exponential rise of technology. So on the one hand we have (in prosperous demographic areas of prosperous nations), a fairly dramatic slowing of the actual biological 'turnover rate.' Parents are even further removed in age from their children than they once were. At the same time, the pace of change has sped dramatically, which must be more difficult for these older parents to cope with and educate their children about than it would be were they themselves younger, and so children (IMO) - more and more frequently, and at younger ages - turn to their peers for help and guidance in the technical skills and the observance of social mores and away from their parents, who seem old and out of touch (even more so than in previous years).

This seems to me to be one of the root causes of the many forms of breakdown in the family unit, the extended family unit, the parent-child bond, and ultimately perhaps the crime rate, the feeling of alienation and depression experienced by more people now than ever, and a host of other social maladies. Just a theory of mine, but it makes sense to me. Any thoughts on this subject?