Difference between "On your mark, get set, go" and "Ready, steady, go"

The Oxford learner's dictionary does indicate that there is a dialect difference for ready, steady, go (see idioms):

ready, steady, go! (BRITISH ENGLISH) (also (get) ready, (get) set, go NORTH AMERICAN ENGLISH, BRITISH ENGLISH) what you say to tell people to start a race

I've always understood ready, steady (or set) go to be a more generic form of on your mark, get set, go, and I'd be inclined to use it in more relaxed situations perhaps. The latter feels more specifically like a race.

In athletics (back in school, in Australia) they used to drill us on the start of a foot race that on on your mark, you'd put your toe on the line, on get set, you'd crouch down (and stick your bum in the air), then go.

I've always associated Ready, steady... primarily with [younger] children.

On your marks... (and more 'formally,professionally', Take your marks...) seem to me far more appropriate for older competitors.