@Ridgerunner has the right of it. I'm in a lot of pain right now, and I'm self medicating, which honestly doesn't help. Will keep this brief.
You are playing the odds. The studies all agree that calcium toxicity is progressive. The studies all agree that hatchlings are most susceptible, then juveniles, then roosters of all ages, then less productive hens.
The studies largely agree there is an (unknown) genetic component.
I liken it to smoking. No one can honestly tell you "that cigarette will give you lung cancer, or mouth cancer, or throat cancer, or whatever". On the other hand, anyone with command of even basic statistics can tell you that the more often you smoke, the longer you smoke, the earlier you begin smoking, the more likely you are to develop one of several cancers. That's statistics.
Excess calcium is the same way, with the very young the most susceptible - their bodies just aren't that "put together", and thus more vulnerable to damage during their formative weeks.
Now, having said that, I "play the odds" in my own feed management, mostly for reasons of cost. All my birds get a high protein (24%), low calcium feed for their formative weeks (8-9) when they are most vulnerable to nitruional deficits and calcium excess. After that, they join the adult flock, where I combine 24% protein, low calcium grower with 16% high calcium layer and end up with a 20% protein, 2.8% +/- calcium mix for my mixed age, mixed gender flocks.
But I do this knowing that almost all of my roosters will be culled and on the dinner table within 12 more weeks - not much time for that extra calcium to build up in their system. My "best" roosters will get a year - long enough that I can find signs of calcium build up internally, but not severe, and with no external presentation.
MOST OF THE TIME. My hens are all moderate to high production, or they get culled early. The old one get till second molt - 30 months.
This is NOT a management style well suited to pet chickens. It involves educated risk taking. and, as with any time you step up to the table and rolls your dice, there are no guarantees.
If your flock plans are similar to mine, rapid turn over with short to moderate time frames, then the cost savings in feed may exceed the losses due to poor health/body condition. That's the same equation I evaluated for myself. If your flock plans more resemble pets or long term layers, with a time horizon of five or seven years in a mixed flock, the math would not add up to me. These are "gut odds", there's no easy formula, jist a sense of the thing from the literature and from limited experience.
