A whole year older than your friend, huh? Are you sure you really want to use this stat as a basis for arguing your point?

Seems kinda silly, or rather, immature, to me.

And apparently, you are taking offence to something she said, when you said something to her that offended her? And if you are so tackful in your speech so as to come across as inoffensive, yet effective for her, then why are you garnering the same response from her?

Sounds like you've changed the rules a bit, not the least of which is thinking you are so much more mature (or superior, possibly, in her mind?). Regardless of whether you leave this fact out, it would still come across LOUD AND CLEAR, just as it does to me.

A whole year...wow

If you just can't do it anymore, then let her go. It's that simple, really. Stop antagonizing each other, and for God's sake, stop trying to control how she feels.