On the night in which Dean was born, he slept in Mary's arms. She wouldn't let the nurse out him in the crib beside her. She only trusted herself and John with the sleeping baby. Mary herself didn't fall asleep until it was silent in the hallway.
When Dean is 3 years old, he told his mommy that there was monster in his closet one night. A monster with yellow eyes. Mary sat at Dean's bed every night for almost 3 weeks until John said that 3 weeks was enough. Mary was reluctant to leave, it was 9 years since the yellow-eyed demon said that he was going to collect something, but Mary knew that if she sat there longer, Dean will think that something is actually there. And he must not know that's true.
When Dean is 8 years old, he does his first salt-n-burn. He can't stop staring at the fire. All he can see is his house on fire, with his mother inside. He starts shaking but he can't stop staring until John forces him to turn. When they're walking back to the Impala, Dean gets very angry and decides that he will not rest until the thing that killed his mom is dead. He feels more like man already.
When Dean is 16 years old, he drives for the first time without his dad telling him what to do. John slouching in the passenger seat beside, holding on his side where the blood is spilling out and Sam is in the back with a nasty head wound that looks like it will need a professional to look at it. Dean makes it back to the motel room so quickly, and not hitting anything, he almost amazes himself. He would be amazed if his family was dying in the car with him.
When Dean is 22, he starts to do solo hunts. There's no Sam anymore to watch out for so he decides to give it a go. He thinks he could do this for awhile until he has to kill a demon that calls itself Sam. Dean then decides that it's time to go back to his family.
When Dean is 26, his dad goes missing and not Winchester missing. He won't answer his phone, won't call any hunters and won't call his own goddamn sons. That's something a Winchester would never do. It's one of the rules. Always let your family know where you are and that you're safe. After not hearing from him for 3 weeks, Dean then decides it's time to get Sam.