The process you've described is basically the informed consent model used by the most lenient areas of the US for transgender care, and exactly the kind of process puberty blockers are used to support - they delay puberty until a kid is old enough to decide for themselves whether or not they want to go on HRT or let puberty happen naturally (usually at the age of 18), in which case all they have to do is stop taking the blockers. The issue with requiring that long wait time for puberty blockers themselves is that by the time somebody realizes they're transgender, it's usually because they're suffering psychological harm from the effects of puberty.

If you're 18+, in order to get HRT (which is different from puberty blockers), under an informed consent model you usually need: a written note from a therapist or psychologist saying that you've consistently had this desire/an official diagnosis of gender dysphoria for 2+ years, plus the written consent of at least 1 doctor who confirms that you have been informed of the effects of HRT and are still wanting to do it. Some states have a more relaxed model specifically for adults that just requires that their doctor has told them about the effects of HRT, but that's the requirements in the states with the easiest regulations. If you start the process at an early age, your doctor might prescribe you HRT as early as 16 (usually in cases where patients have consistently said they've wanted HRT since prepubescence), but most often you have to wait until you're 18. If you're somewhere like the UK? Then you have to do all that, and be put on a potentially 8+ year long waiting list to see a doctor who can deny you with no justification, and a bunch of other hoops. At one point doctors could deny you if they didn't think that you'd be hot as a woman.

There's a lot of misinformation and half-truths surrounding puberty blockers (and transgender healthcare in general), but they were originally developed in the 70s and have been in regular use since the 80s to treat a condition known as precocious puberty - basically, when puberty happens at like age 6-10, which can have harmful effects on the body and cause psychological issues. People didn't care until about 10-20 years ago when people realized they could also be used to delay puberty in transgender kids until they were old enough to decide for themselves and avoid potentially permanent unwanted changes to their body that could cost thousands of dollars in surgeries and medicine to change (not to mention years of therapy). An 18 year old girl can get breast implants or a full body tattoo on a whim, and nobody really cares. But the drug a minority is using to pause bodily changes that could potentially have a permanent negative effect on them? Suddenly it's "untested" and "causes permanent harm to kids' bodies" even though they've been in common use for 40+ years.