Fred and George were inseparable.
When they were born, Mrs Weasley had to knit sweaters with their names on them to tell them apart.
When they were one, they took their first steps on the same day, and they went to each other.
When they were two, Bill tried to pick George up and leave the room. Fred wailed at the top of his lungs, and George wouldn't stop kicking in his arms. Charlie thought it was hilarious that Bill had a bruise for several days afterwards.
When they were three, they had a new sister. To make room in the house, Mrs Weasley asked Fred to move in with Ron. Fred threw a fit, and George clung to him like a lifeline.
When they were four, they got seriously sick for the first time. Once they got to Hogwarts, Angelina and Katie would groan when either one sneezed, because when one twin got sick, the other went down too.
When they were five, Fred turned Ron's teddy bear into a spider, and George found a hiding place from their mother. It was their first prank, with many more to come.
When they were six, their parents bought twin beds instead of the one they shared. Neither of them slept well the first night they were apart, and they woke up huddled together in the corner of Fred's bed the next morning.
When they were seven, Mrs Weasley tried to send George to Aunt Muriel for a week as punishment for scribbling on Percy's books. He came back two hours later when Fred wouldn't stop screaming and half of Aunt Muriel's living room was destroyed by a very angry twin.
When they were eight and visited a muggle village, two kids threw mud at George and mocked him for asking what a soccer ball was. Fred kicked them in the stomach and made them burp up slugs with accidental magic.
When they were nine, they were offered a new broomstick. They turned it down; they didn't want each other to be stuck with the old broomstick. So, the new one went to Ron.
When they were ten, they got their Hogwarts letters. Fred's letter came five minutes before George's, and in those five minutes, Fred refused to leave if George was a Squib.
When they were eleven and arrived at Hogwarts, they nabbed a blank piece of parchment from Filch's office and discovered its secrets when George insulted it right back after it offended Fred. The Marauders thought they deserved to learn their secrets.
When they were twelve, Fred ended up in the hospital wing for falling off his broom during a Quidditch match. When Madam Pomfrey tried to keep George out, he punched himself in the face and claimed he was injured.
When they were thirteen and met a scrawny, skinny boy with broken glasses and a lightning scar, they silently agreed that they had a new little brother.
When they were fourteen, Ginny was taken down into the Chamber of Secrets. They slept in the common room that night, Fred's head lolling on George's shoulder, their eyes filled with worry and unshed tears, sure that they had lost their baby sister.
When they were fifteen, they gave Lupin a pounding headache right before the full moon by finishing each other's sentences and having silent conversations behind his back. They could have sworn they saw a flicker of a smile when they apologized in unison, however, because, little did they know, James and Sirius would do the same thing.
When they were sixteen and Cedric and Harry's names came from the Goblet of Fire, the twins thought it was for the best anyway; they didn't want to compete in the tasks alone.
When they were seventeen, they had always planned on leaving Hogwarts, but George decided it was time when he came back from a detention with a bloody hand and Fred threatened to curse Umbridge.
When they were eighteen, they finally achieved their dream. On the opening day of the joke shop, Fred wanted George to walk in first and George wanted Fred to. They walked in together.
When they were nineteen and George lost an ear, Fred had a panic attack as his head throbbed with pain in the middle of the battle. He thought his brother was dead.
When they were twenty, Voldemort fell to the ground, never to rise again. And when George was hunched over on the cold ground, sobbing and pounding his bleeding fists on Fred's still, pale figure, they finally understood the risks and sacrifices of a war.