Not sure what growing zone you're in, but I'm guessing from your username that you're in the UK. Flame Trees, aka Royal Poinciana (
Delonix regia) are a tropical tree in nature. Here in the States, they're usually only found outside in areas like south Florida and southern Texas. I'm originally from Florida and can confirm these things are everywhere down there! However, they are only hardy down to USDA grow zone 10, which is 30-40F (-1 to 4C). You will need to bring the tree inside every fall/winter and keep it in a sunny area. In the spring/summer however, you should have it outside in full sun when the temperature gets consistently above 50F (10C).
I have the same tree, and mine has been growing from a seed since October of last year. It was inside that whole time until I moved it outside this past April when we warmed up enough here. I'll be bringing it inside again this October.
Yours is too young to start cutting on. These trees can take a while for the trunk to start splitting into more than just one long growth, and you definitely need to wait for the trunk to start hardening as well. What you're going to see next, and may have seen already, is when the trunk starts to harden, it goes from green to brown starting at the root base. The leaves on the lowest branches will turn yellow and fall off. Then the branch itself will fall off. Don't panic, as this is normal. I would not personally do anything with that tree for probably at least another year. If you wire up the trunk while it's still green, you will likely cause damage.
Here's a photo of mine for you. It's in a 3 gallon pot, and the trunk is currently about 3/4 inch thick (just under 2 cm). It's developed that gentle "S" bend in the trunk from being outside in the wind this year. Good luck with yours, and enjoy it! Just know that it will be a while before you can really start doing anything to it.