Rooster keeps attacking chickens?

[CochinBeauties]

My bantam rooster, who is 7 years old keeps attacking my 6 month old chicks. One is a miniature (dark cornish bantam) as well and she tries to fight back with him, the other one (a rhode island red) just runs away.
Why does he keep attacking them? We normally dont let them around each other because of this. Will he stop? When?

 

[cypressdrake]

Sometimes they'll stop once the pecking order has been established. If it goes on for days or he starts drawing blood, I'd remove him or separate them.

 

[sumi]

If your rooster is grabbing them by the backs of their necks he's trying to mate with them and they are probably resisting? Just throwing out a guess here. Chickens mating, especially when the hen is unwilling, is not for the feint hearted.