One of Thor's first memories is of Loki getting him in trouble. They're very, very young; he's probably only about 174 and Loki had just turned 62. They were goofing off, kicking at each other and trying to pinch the other without them noticing. Then Loki had tripped and fallen down the stairs to the throne room.
Naturally his brother's screams had brought their parents running, and Loki cried that Thor had pushed him. As punishment he had to sit in the corner of the dining hall, alone and absolutely silent, every day for two weeks. Being so young, he thought it was torture.
When they were a little bit older, about 406 and 518 respectively, Loki had caused a small stampede of bilgesnipe. Thor had been practically glued to his father's side, hanging on to his every word as he conversed with the visiting king of Anaheim, when shouts and screams were heard. By the time they got outside the stampede had passed and all they was were the fleeing hindquarters of the repulsive beasts. But the damage had been done.
They found Loki smiling sheepishly, observing the trampled carts and damaged buildings and homes. It had been nothing short of a miracle that no one was hurt or killed in the stampede.
"Apparently they don't like to be milked," Loki had told Thor later, as means of an explanation.
Then, when they were maybe 886 and 774 Loki had snuck into his bedroom and shook him awake with a finger to his lips. He was grinning that mad grin of his, the one that he thought really made his brother seem insane, and Thor knew they were about to get in trouble. Which was just fine with him because that meant they were going to do something that required breaking the rules.
They'd snuck into the servants' quarters, perched high in the rafters, and watched the women bathe. They were only caught when Loki reacher over and pushed Thor off balance, sending him tumbling down into the water. The culprit had had plenty of time to escape through the skylight in the following commotion, but he hadn't. Instead he'd sat on the beam and laughed until he cried, and when the guards were brought in to see what the problem was, he dropped to the ground and stood beside him while their father yelled.
There had been thousands of other incidents while they were growing up, including (but most certainly not limited to) Loki turning Sif's golden hair as dark as his own, and the destruction of their great-grandfather's prized helmet. Growing up This had lost count of how many times Loki had tortured their tutor or pissed their weapons trainer off to no end. But all of them had made Thor smile in the end, and even when he was on the receiving end of Loki's schemes it never diminished the love between the two brothers.
This is what Thor thinks about when people call his brother evil.
And these are the memories that come to his mind when he is forced to leave his brother's body behind on Svartalfheim.
Alright, so I did a little math and figured out that when Asgardians are about 58 years old they are the equivalent of a 1 year old human child, if the average lifespan of a human is about 85 and the average Asgardian lifespan is 5000. I know I'm boring you guys with this, but based on that math, for Thor's three memories their ages are about 1 and 3, then 6 and 8, and 15 and 13.