Sounds more like ownership annotation than generations. Generations basically takes advantage of the fact that recently allocated memory is much more likely to

Sounds more like ownership annotation than generations. Generations basically takes advantage of the fact that recently allocated memory is much more likely to be deallocated sooner - ie. it's run time/age based. What you're describing with arena is more like ownership where siblings can't outlive ancestors - ie. deallocate when parent/root (arena container) is deallocated.