Still a pullet. Wyandotte roosters have such a different feather pattern and by 20 weeks you would be seeing definite differences. The tail feathers would be black by now. The combs would also be a dead giveaway by now too. GLW hens are going to outweigh your BR by a good 2# so don't let her size get in the way.
Wyandottes are going to be slower to start laying being a DP breed. My one GLW from this year started at 25 weeks. She had a nice read comb and waddle for about 2 weeks prior. Yours don't appear to have much color yet.
First time I saw a GLW, I was hooked.
Last edited by Left Hand Percherons; 09-05-2013 at 11:32 AM.