If you aren't
being pushy (keep it fun and something the kid wants to try, not a chore-to-be-done because "you must
learn how to code!") then six isn't too young.
I'd avoid anything that needs loads of typing (at least until/unless typing is mature enough to be not frustrating when needing to be accurate and free of typos, and then there's still "thinkos" like missing vital punctuation/brackets) but you might look into Scratch on (or off?) the Raspberry Pi which is quite powerful, with the ability to read/write data inputs/outputs and even (however you see it) process forking or OO:
There are other such building-block languages (literally?
) and platforms (I've yet to get my hands on a BBC Micro:bit
but if you can then it's maybe worth a look), but the other opportunities in a Pi seem to make it versatile enough that what little you spend on it won't go to waste if you daughter can't/won't code yet/ever, and 'forces' you to turn it into a media-server or something else for which there's various pre-prepared builds for.