If all are laying already except this one, you are doing better than me. With ten dual purpose pullets, I usually get my first egg somewhere around 18 to 20 weeks of age. Usually by the time they are 23, half of them are laying. They are usually all laying by the time they are maybe 27 weeks old. I have had some go much longer before they start. You are doing well. Congratulations.
I got some green eggs from another forum member and hatched some EE's last year. The three pullets all started laying before 23 weeks, but two of them laid brown eggs. That's the problem with EE's. They are mixes and you are never sure what you will get. But the green egg layer has given me a lot of large green eggs, laying about 13 eggs every 14 days. She went broody and is currently raising 6 chicks. I'm quite pleased with her. Hope you are happy with yours.