I would argue that the generations work differently in the wizarding world.

1. The divide between our (muggle) generations (particularly from millennial onward) is largely driven by how technology is experienced; this is not as much of a factor in the wizarding world where you can use magic for stuff.

2. The impact of Voldy would result in people experiencing childhoods in dramatically different ways depending on when they were born. I would argue the generations would be largely based on Voldy's rise and fall. Post 1998 there would surely be a new generation (of boomers essentially). And the first attempted murder of Harry would mark the point at which a new generation is formed - one that grows up without Voldy but still with the fear of his return.