Well first off, Fred and George just sounds catchier than George and Fred.....
and I'm with you guys. I think that Fred is older because...well......he just strikes me as the older one.....*shrugs* go figure
Anyways, as for the telling apart thing...maybe Mrs. Weasley put a spell on them that turned one pink and one blue?
And this people, has been a look into the twighlight zone2(aka my brain)