Essentially an offshoot of a Dyson sphere. I‘ve always wondered about the mechanics of those. ;-)

Pregnancy is an inherently dangerous for us, mammals.

I’ve read of lion cubs in breach position who would have died if not for veterinary assistance. And, of course, the whole body of literature on medical problems in domesticated animals.

As with all population-wide things, it’s a range: some bodies mature sooner, some later in life. The number 25 is a convenient mid-range estimate.

Let’s take an example that we can actually see, and use it as a rough marker for physical development: wisdom teeth. The majority of people get them between 18-26. In some instances, however, the wisdom teeth don‘t erupt until the age of 40! This indicates that the individual’s body is still developing at that age.

Hope this makes sense.

I would have answered “dinosaurs!”, but your explanation is considerably more detailed. ;-)

Gold is very soft, so the initially polished shiny surface easily accumulates abrasions and scratches - and becomes dull. In fact, lower purity alloy, mixed with a harder metal, would maintain the sheen longer than pure gold.

A related point of interest: gold nanoparticles are dark red color, not, well, golden.