Nope, not too young. Green stems are sometimes too soft and/or the stem joint (to another stem) are too fragile when they are new.
Otherwise, the deal is that the bark sometimes separates easily from the wood. This is during spring to a bit (say 6 weeks) after the summer solstice. Don't wire/un-wire during this period and you'll be fine with just about any species.
Btw, watch out for those thorns!!
How do you do that?I’d let them keep growing to thicken the trunk. Maybe also place a tourniquet under the soil line to get some trunk flare going.
If you have some larger-gauge bonsai wire, you can wrap it around the trunk and twist it tight. As the tree grows it will swell above the wire and give taper to the trunk. It will also likely shoot roots above the wire, too.
And since not mentioned kill tree if not removed soon enough and leave constriction at place above roots.
With my luck.. Ill kill it.. LOL... 100% for sure, no doubt. I guess I'll just pray to God each day that the trunk gets a good taper. OT maybe try it one one of my trees. I have 5 of these Umbrella Thorns. I could try it on a younger one. Home many wraps of wire? Just a few I assume?