Usually the bigger the cutting the better the odds it will root. So I would not worry about it even though the trunk is mature wood, it will root from the sides and cambium layer.

Cool! They do root easier than smaller branches for sure.
Tally HO!

Awesome! I was a little worried because its getting late into the season. Now, do you think they would root faster being out in the sun or being in a hot greenhouse?

someone down under recently had a tree sized cutting.

I was told by an experienced grower that the woody cuttings will take a long time but will root. In fact the phrase he used was "put in the back alley and forget about it."

I'm about to find out if my cutting is going to survive (spring here now). Here's what I have done... cut it straight across, not at an angle, applied rooting gel and put it in a soft drink bottle with 100% perlite, added a tiny bit of water and covered the opening up with a plastic bag to stop most of the water from going in. Planted it in the ground 2 weeks ago. The tips are slightly soft, not shrivelled and still green. I'm hopeful!

Here is a link that might be useful: My large cutting

Yeaaaa, I got my fingers crossed for it. Since it is spring by you now that improves it's chances. Keep us informed how it does. Peg