Up to what temperature is this jacket appropriate?

Assuming you mean DOWN to what temperature, not very low. It's really just a slightly thicker than usual raincoat, so on its own it won't insulate that well. Depending on how warm in general the young 'un in question is, I would guess down to about 45F. With layers, of course, you could go much colder. If you did in fact mean up, then knock yourself out. The "fur" comes off, so wear it until it's hot enough to make you sweat inside, at which point it's probably time to strip a layer. Maybe mid 60's?
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