15Fred was born first
Ever wondered which Weasley twin is older? No need -- J.K. Rowling confirmed on Twitter in 2015 that Fred is the older of the two. Fittingly, Fred is more independent than his brother, and he tends to take the lead both in their relationship and
in their interactions with others. He’s also the first twin to crack a joke in the movies. When Harry sees the Weasley family at Platform 9 and 3 / 4, Mrs. Weasley is in the middle of herding her children to the train. Fred pretends to be George and is mock offended that his own mother can’t tell them apart, before cheekily telling the truth just before dashing through the barrier.
Rowling has stated that she thought that the twins’ birth order was obvious. This might be because F comes before G in the alphabet (would Mrs. Weasley have done that on purpose?), or perhaps it’s because of their personalities.