"Boy Turning Four" joke

A boy was turning four, and his dad said he'd give him whatever he wanted for his birthday.
The boy replied,' Can I have a tractor this year?"
His dad said' Yes, of course.'
That year the boy got what he wanted.
The next year, his dad went to him and asked him what he wanted for his birthday this year. He said "Can I have a bigger tractor than last year?"
The dad kindly said yes.
Three years had passed and it was the boys birthday again and his dad asked him what he would like this year, again the boy asked for a tractor.
He got the same present each year. Eventually the boy became 18, his dad walked to him and asked what he would like for his birthday. The boy replied "Can I have a walkman?"
The dad was surprised and agreed.
The boy got his present and was walking down the road, when he smelt smoke. As he walked further, the smoke became thicker and thicker. When he got further he found a building was on fire.
He dropped his walkman and ran towards it. He opened the letter box and started sucking out all the smoke.
The firemen were wondering what the hell he was doing. The boy kept sucking out the smoke out through the letter box.
Eventually the smoke went, and he stopped. The firemen ran towards him and said "How did you get so good at sucking the fire out?"
The boy replied "Well, to be honest I'm and ex-tractor fan."