Perhaps I shouldn't have mentioned he has autism as it's not relevant to this thread- I was just trying to give background as to why this is a new problem for us. I'm not really sure what age it normally becomes something you deal with.

I find that giving them an option where the answer can't be NO can help at times. Doesn't always work but it might be a response like "Well we HAVE to go in the car - so do you want me to help you or can you climb up yourself"
This is what I do, so that he had the choice but if he needs me to do it for him then that's the choice he made.

I just wanted to hear what people do from a gentle parenting perspective because it crosses the line of treating a person with autonomous respect sometimes, but at the same time I think being too submissive or wishy-washy as a parent isn't helpful for children either.