Delonix regia question about first cut

So I have 3 delonix regia, one of them had its leaves eaten early on by some insect or somthing however I was able to get it to sprout again and now it's growing strong.They are all under led full spectrum with a heat Matt nearby for residual warmth. I want to cut back my other 2 or maybe one to start but have read they must be 5 years old and have vibrant growth. Mine are doing very well, and I'm wondering if that's true how huge they would be and also, I've already got a delonix that was unintentionally cut back that thriving.....not sure what to do. I'll attach pics of all of themBy the way they are all 1.5yrs old. And I've heard after 1year you can cut back. So much conducting info out there and I don't wanna kill them.

On bonsai a thick trunk is desirable. To thicken The trunk you need to let it grow freely for a couple of years. 5 sounds just about a good recomendation for tropicals.

Is it not a matter of preference?
I more after information concerning the health of the trees and since I already have a tree that was topped by accident within 8 months of sprouting and seems to be doing well. I'm not sure why I would wait 5 years?
Will I not just have smaller trees if I top them earlier?

Obviously there's something I'm not understanding.
Please excuse my ignorance.

It’s a question of ratio: to be convincing as bonsai it needs to look like a grown, old tree. An old tree has a thick trunk, with branches that correspond to that thickness, and a height that corresponds to that thickness. To top these ratios you have to consider the leaf size too to be convincing ; big leaves on a little tree just don’t work/ feel right.

Exactly. Bonsai is about perspective, that in its most basic form mathematically speaking can be explained by ratio. The exact ratio is not as important as the impression you get from the tree. But common beginner guidelines say that the hight of the tree should be 6 to 12 times the diameter of the lowest part of the trunk. So in your case, I guess 5 mm trunk, you can shop down to 3-6 cm tree. But then the leaves will look huge and not at all in proportion to the rest of the tree. I am not familiar with the species, so I dont know how much the leaves will decrease in size. But I think you have a tree that needs at least 10 cm trunk before the leaves are in proportion.

If you like the look of your trunk chopped tree. By all means, just do it. You have allready proven that it can be done so health of the tree is not that much of an issue.
But I dont think it will within your lifetime look like an old natural tree. More like a stick in a pot, a tortured young plant.