Yeah, but he said that as a sales pitch. Remember he was not an engineer.

The “Mac OS X” was more of a brand name than a singular OS. Each major release (the ones with new code names) was essentially a whole new OS. iOS just turned 13, but each year, it’s full of big changes.

I think Jobs might’ve been referring to the actual OS internals, not the brand name. As in, support period. After all, Linux (while not technically an OS) is older than Mac OS X / macOS, but it’s not obsolete. Just don’t expect to get security patches on kernels in the 2.x or 3.x range.