Hi, welcome to BYC!
I agree with @chickens really . Starter or grower is perfectly fine for everyone with OS on the side.
Alternatively, for my mixed age and gender flock.... I use Flock Raiser with 20% protein and offer OS on the side for layers. Don't currently plan on changing any time soon.
Yes, it's a big No No (in my book). The problem with feeding the youngsters Layer is too high of calcium can both stunt their growth and cause long term kidney damage. There is no way to tell how soon your young will start to lay, if they even do this season. We are short on day light here. But even when not short on light, many of my layers (even supposed 16 week starters) didn't start until well after 24 weeks.
And one that started, laid for a month and already quit for the season.
NOBODY wants to deal with multiple feeds.
So what you call POL, are they actually laying? Sometimes with the stress of moving and integrating, laying can be diminished or even quit while they are adjusting to the new environment.
Best wishes!