If you are measuring the current hurd kernel's age as starting from 1990, then the BSD kernels are far older, not younger. The initial release was in 1977, and obviously development started before that.
That said, hurd is essentially abandoned at this point. Even RMS has accepted that it will never be completed, and has said that it really doesn't matter since there's already a free kernel available (linux).
That said, hurd is essentially abandoned at this point. Even RMS has accepted that it will never be completed, and has said that it really doesn't matter since there's already a free kernel available (linux).