Agehaya comments

I've heard that as well (in the past), but I think nowadays the twin born first is considered older.

And as for identical twins "often being like this" as dammit purported...I strongly disagree. While I don't think it's out of the realm of possibility, I don't think sibling rivalry is greater among twins (identical or not) than in regular brother/sister or sister/sister relationships. While it's perhaps anecdotal evidence, I might bicker with my twin, but she's my very best friend. It's my older brother we'd both like to see put down a few pegs. In fact, I've known many sets of twins over the years, some identical, some fraternal, and I can't think of a single set that was ever at each others throats.