Some hens grow spurs, some have tiny ones and some much larger. I currently have 2 of 10 girls with spurs, both on the smaller side, but my old head hen had big, thick spurs that I had to tip regularly since they were curled up towards her body.
And yes they can seemingly grow them out of nowhere, spurs don't necessarily begin growing in adolescence. The old hen previously mentioned went broody once somewhere between 1 or 2 years old, and her spurs began growing in after that.
And yes they can seemingly grow them out of nowhere, spurs don't necessarily begin growing in adolescence. The old hen previously mentioned went broody once somewhere between 1 or 2 years old, and her spurs began growing in after that.