Not in practical terms - by their very nature, registers must be mutated during a non-trivial program. Still - processor instructions are functional by nature: for example, an ADD op requires two register inputs and one register output. The assembly I worked with in university also includes the ability to create callable procedures. So even when designing assembly code, it pays to think in functional terms, although as stated earlier, registers are mutable by nature. My point was the constraints of the time kept developers from making things too complicated, so their programs often followed functional like, simple designs - see the POSIX utilities for example.

Still, Lisp was created in 1958 [0], so it's definitely likely some folks grandparents were programming in it :)

[0] https://en.wikipedia.org/wiki/Lisp_(programming_language)