Then your younger ones are attempting to challenge the older girls for a higher rank in the pecking order by trying to move in on the feed dish. It's a normal reaction, then, for the older girl to put the youngster back in her proper place. As long as the youngsters don't push it, things can go along rather peacefully.
Once in a great while, you will see two hens going at it vigorously with flared neck feathers and even biting each others combs. I've seen stand-offs where they're both just hanging onto each others combs and neither willing to concede. That's a serious challenge, but even one that is that intense will resolve itself.
When there's bullying is when it gets complicated. It usually involves an individual who is experiencing declining self-confidence for some reason. It could be age, health problems, or too many challenges from youngsters. It's usually another individual very close or at the bottom of the pecking order that picks up on this, and begins a bullying rampage. If the hen doesn't stand up to the bully, the bullying can be joined in by others.
I have such a hen right now. Because of her complete and total loss of self-confidence, not just one, but all of the youngest members of the flock and a couple of the older ones bully her so badly she can no longer get enough to eat. When they go after her, two will chase her down and literally get onto her back as she is crouching in submission and stomp her and peck her. She's scared to even roost at night. I've given up trying to intercede and she now spends days in her own safe enclosure inside the run where she can still interact, but safely with the others. I bring her inside at night to sleep in a crate in the garage. She seems to be thriving now, albeit in an artificial arrangement.
Sadly, bullying is a part of the pecking order, too, but harder to deal with.