Moving from carrycot to sit up pushchair

Emma

So the words may be different in US to UK, lol, but hopefully you get what I mean!! Little one is in carrycot, like the lie flat bit of our travel system. He's getting quite long now though.

How soon can we use the sit up chair instead? Is there usually an age / weight minimum that I need to check with the manufacturer? Or is it things like being able to sit up unaided?

Thanks! We have the uppababy vista