We started explosive child when DS was about 3.
Honestly, I didn't think it would work because he was so little, but the very first time I tried saying 'that seemed to be tough for you. What's up?' it just transformed the interaction between us because he didn't feel blamed, didn't shut down and get defensivr.
Ditto with coming up with solutions - just the sense that it was, basically, up to him to figure out what to do. That we'd help him and might have suggestions, but that he was the one who had to live them, so they had to work for him. It made him so much more willing to try things.
It's not like everything is perfect, but I give Ross Greene about 1/3 of the credit for DS being, generally, a happy autistic child.
FWIW - we never really took the low demand explosive child approach. There is stuff we let slide, absolutely, lots of it, but the basic idea was always 'this thing is hard for you. Ok. It is important though. So let's figure out together how we can make it work'.
Hope that helps.