First of all, being trans isn't a choice, so there are no decisions being made as to whether to be trans or not at any age.

Also, let me spoon feed you the way transition works for a child since you either can't be bothered to do basic research or probably get all of your ideas from Fox et al.

For prepubescent children, there are no medical procedures taking place. Transition is social and involves trying out new names, dressing differently, different bathrooms, and changing pronouns. All easily reversible.

At puberty, you can go on blockers. These were initially invented for cis kids with precocious puberty and nobody raises an eyebrow about those cases. This isn't some black market thing. A doctor has to prescribe them and a parent has to sign off. Also reversible. Keep in mind that natural puberty is not.

Then, usually after years have passed, you have gone through social transition and blockers, sometime in your teens, you can begin cross sex HRT. This also requires approval from a doctor and psychiatric professional, as well as parental consent.

Finally, after years on cross sex HRT, then we can start to get into surgeries. By this point, you are at least mid teens. You usually need multiple letters from psychiatric professionals to approve these procedures. Bottom surgery also is not the first surgery a trans person gets and is reserved for people over 18 except for the most exceptionally unwavering cases with a very long history of outwardly demonstrated gender dysphoria dating back to toddlerhood, in which case it's still going to only go down to 17 or maybe 16.

Also keep in mind that for bottom surgery, you need a sufficient amount of physical development of the genitals to even have enough material to work with, so it's simply not possible on people who have not reached a certain stage of growth. This is why for metoidioplasty, you need to be on testosterone at least a year, if not two and you can't just do penile inversion on a little baby peen and expect good results. No doctor in their right mind would perform these procedures on someone who is physically a poor candidate. In order to get approved, you have to have a consult where the doctor examines you and decides what procedures would be a good fit. There are even a lot of trans adults who aren't a physical match for certain surgical techniques.

If you don't get it at this point, I don't know what to tell you. And no, waiting until 25 would just lead to a ton of suicide.