Three week old still with very limited ffeather development, should I be worried?

I have a chick who is three weeks old today. She/he seems to have stopped developing with just the limited wing feather growth. She/he eats well and plays when not sleeping. Its been cold so hiding in a warm spot seems to be the preference. Should I be concerned that this little one may be ill? Poo seems normal.

This was just taken a few mins ago. Three weeks old today.

 

Im not concerned about the sex, just the health. The mannerisms are more like a female. Unfortunately I dont have but the one hatch from this brood so no comparison chick exists only experience from other previous hatches.

 

I am the brooder

 

This little one was a lone hatch under a broody hen. I brought her inside to stay with me. This is how I am noticing the slow feather development.

 

I had a little guy, my first chicken, who I raised with me because I didnt have a coop or others for him to live with. I enjoyed him so much. He was my buddy. I got others because I was advised chickens dont do well alone. Well he never completely crossed over. He played with the others during the day but spent the evenings and nights in the house with me. Anyway, he died. I am wanting to raise another as I did him. This little one was a lone hatch and mama(s) are still one eggs. I figured it would be a good chance to try again.