You can use this position from Newborn, up until 15kg. Make sure you spread the bands evenly into the corners of their knees, creating a bucket seat which is optimal for avoiding hip dysplasia. Their neck and head can be supported with one of the bands, simply place ear to your heart and place the band across their head so face is still visible.
Please be aware that the carrier should feel very firm to begin with to provide the support necessary. Your baby may feel like they sit too high, but the bands will stretch with wear and they will drop to a comfortable height if you have the correct size. You can raise the position of the crossover on your back which will also bring baby down lower at front. Twist bands at shoulders if the carrier begins to feel loose, or wash as per our instructions to regain firmness.