>>936971572 (OP)there won't be one. global human population of people under 30 peaked this year at about 3.1 billion people
new genres and new "big thing"s are a function of huge rushes of new minds to scoop up. Old people don't gravitate to new things because they already have established interests in old things they picked up when they were young, plus they're busy with work and raising families etc.
there just won't be the kind of novelty that we saw in the past, those days are gone. In general a human population where the median age ticks up closer to like 60 is going to be a much more lethargic, static one. Young people are the ones with energy and innovation and young people are dying off, the number is literally going backwards now.