Well, he did say OS X (today named macOS), which is built on top of Darwin. Darwin itself is a combination of two things: XNU and BSD. The BSD parts originally

Well, he did say OS X (today named macOS), which is built on top of Darwin. Darwin itself is a combination of two things: XNU and BSD. The BSD parts originally came from 4.3BSD, and were later upgraded with code from FreeBSD, with many userland tools from NetBSD. So by that token, the macOS lineage goes back to 1977, the year BSD was first released. FreeBSD is based on the original BSD distribution. While FreeBSD got rid of all the AT&T code, you could also make a good case that since it derives from AT&T UNIX, its lineage goes all the way back to 1973. XNU is not that old; it was developed at NeXT in the 1990s, and is based around Mach, a kernel first released in 1985.