My understanding/recollection of the early history of Linux is that it owed a significant debt to Minix [1] which was developed by Andrew S. Tanenbaum [2] at age (wait for it) 43...
It owed a significant debt to MINIX mostly in that Linus did his work under MINIX while he was getting the kernel to something usable. Code wasn't copied and architecture was quite different (Tanenbaum had mostly bad things to say about the design of Linux).
1. https://en.wikipedia.org/wiki/MINIX 2. https://en.wikipedia.org/wiki/Andrew_S._Tanenbaum