Am I being too uptight about this?

[gcj]

I don't think you're being u[tight. I think that that behaviour is unacceptable in your house and you have every right to enforce that. If it's unacceptable there should be consequences for their actions. Since the other boy is older, sit them down together. Tell them exactly what is expected and what changes need to take place. If they cannot remember these rules they will lose privileges or whatever you choose as punishment.
I have a 6 1/2 year old son and can totally imagine what you're going through. You have every right to want it to stop. Boys will be boys, but boys must also learn when and where is appropriate at to respect other people.
End it before you lose your mind! Good luck