I have been trying to avoid saying this to DS1 as being a first-born myself I have heard it many a time. But today, he really made it difficult. Jack pushed his brother so I said

Me: "Jack, you must be gentle with Tom".
Jack: "And Tom must be gentle with me"
Me: "Yes he should. But he learns from you so if you are rough with him he thinks it's ok and then is rough with you"
Jack: "Well I learn from him too. So if he is rough with me then I think it's ok and am rough with him".

Hmmm, I admit it - I said those words I dread - "But you're older - you know better". Yep, sounded just like my mum!!