The only way a cage can be too big would be the bar spacing. GCC are so small that 1/2" is ideal. That one looks like the way most cages that size are, 5/8". So barely over 1/2". I think it should be fine. It's unlikely that your bird will try and stick their head through the bars anyway. Some do, which is the reason for the caution, but I don't think it's too common. At any rate, I think they'll be fine, but if I had a GCC I'd go with a flight cage which comes standard 1/2" and spacious interior as well.