... what... Chins live for 15-20 years, and less than 1 year is too young, and over 2 years is too old? ... Something about that doesn't sound right...
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I know it's totally inaccurate, but I was tempted to just multiply by 5... (15-20 Chin years = 75-100 human years?) ... but that gives 1 chin year = 5 human years, 2 year old chin = 10 year old human, so that can't be right lol...
Someone told me that Chinchilla's reach their maximum size at 1.5 years old or so... if that's true, then I do see why pregnancies under 1 year old might be bad! Logically, pregnancies DO take a toll on a body, so surely it's only common sense to let them finish puberty/ growth, before letting them get pregnant?
Also, offhand, if an organism can safely give birth up to 8-10 years old, having it's first pregnancy at 4 sounds fine? ... I think your friend has it backwards, and I'd assume that it's optimum to let chin's get pregnant a few months after they have reached maximum growth? In other words, 2 years old is about the optimum EARLIEST time?
Could be wrong there, I'm no biologist, so the whole "let them finish growing before getting pregnant" thing is just a guess on my part... please tell me if I'm wrong!